NT’s 5e Houserules

House Rules and Clarifications for D&D 5e

Introduction: What and Why?

First, the what. Here's a breakdown of how I format each of my house rule suggestions: 

Title of Rule Change

The suggested house rule is in italics. Deprecated alternative or additional suggestion is in strikethrough.

An explanation of why the change is needed and other possible relevant issues is in plain text.

The title's highlight is an approximate indication of how necessary any particular house rule might be, from orange (vital unless the situation never comes up) to green (relatively optional), with many of these rules falling somewhere in between. Some of the more vital house rules use a less "urgent" highlighting when the existence of a significant number of other options alleviates the issue, as is the case frequently with spells and feats. Also, some of the items here are clarifications of the rules. These are not highlighted. Where applicable, the relevant rules are linked on D&D Beyond

The broader reason why is more complicated, but far from unfathomable. None of the changes suggested here are absolutely necessary. But D&D is played to have fun, and some parts of the game, when played as written, are not fun. These flaws may come to light immediately, shortly, or after a while. But the latter is actually the worst case: you play a character for a while, are attached to the character, but one day realize that you don’t enjoy playing that character. It's often difficult to articulate which parts of the game are tedious, or how to fix them, so even though you realize you have little to add to the game in certain situations, you still spend much of the game quietly waiting for the fun parts. These are annoying road-bumps in a game that one plays to have fun, and the goal of these house-rules is to avoid the annoying road-bumps and keep the focus on having fun. In that spirit, most of these fixes aim to be simple tweaks, but I have included a couple of larger rewrites (such as the Elemental Monk), should players and DMs agree to use them.

Useful Links


Table of Contents

Introduction: What and Why?

Useful Links

Table of Contents

House Rule Zero

Alignment & Ability Scores

Against Rolling Ability Scores (and HP)

Alignment

Charisma: Previously Acquainted NPCs

Dexterity: Not the Only Initiative Bonus

Shifting Important Ability Scores

Strength: Additional Benefits

Intelligence: Additional Proficiencies

Wis: Passive Perception is Check Floor

Races & Backgrounds

Additional Backgrounds

Alternative Background Feature

Background Trinkets

Changeling

Beastfolk

Darkvision sees as if Dim Light

Darkvision only for Undergrounders

Dragonborn: Subraces

Dragonborn: Breath Weapon Effect

Secondary Backgrounds

Variant Human

Warforged

Classes

Multiclassing

Additional Classes

Additional Save Proficiencies

Barbarian: Path of the Brawler

Bard

Bard: Lore: Cutting Words

Bard: Magical Secrets

Bard: Superior Inspiration

Better Ranger & Druid Beasts

Cleric: Discipline of Life

Cleric: Domains

Druid

Druid: Archdruid

Druid: Circles

Druid: Wildshaped Dragonborn

Engineer

Fighter

Fighter: Action Surge

Fighter: Arcane Archer: Arcane Shot

Fighter: Arcane Archer: Arcane Shot: Curved Shot

Fighter: Champion – Hit Dice

Fighter: Eldritch Knight – Spell Components

Fighter: Eldritch Knight – War Magic

Fighting Style

Fighting Style: Great Weapon Fighting

Fighting Style: Dueling

Monk

Monk: Perfect Self

Monk: Way of the Four Elements

Paladin: Oaths

Ranger

Ranger: Beastmaster

Revivify Beast (Level 2 spell, ritual)

Ranger: Hunter

Ranger: Hunter: Horde Breaker

Ranger: No Spellcasting Focus

Rogue

Rogue: Reliable Talent

Rogue: Sneak Attack

Rogue: Swashbuckler: Rakish Audacity

Starting Gold

Sorcerer

Sorcerer: Favored Soul

Sorcerer: Quickened Metamagic

Sorcerer: Sorcerous Restoration

Sorcerer: Wild Magic

Warlock

Warlock: Pact Blade

Warlock Patron: The Machine

Wizard: Illusory Reality & Minor Conjuration

Feats

Additional Feats

Feat Point Purchase System

Charger

Crossbow Expert

Elemental Adept

Grappler

Great Weapon Master

Intensified Dragon's Breath

Jack of All Trades

Lucky

Martial Adept

Medium Armor Mastery

Polearm Master

Savage Attacker

Savant (New Feat)

Sharpshooter

Shield Mastery

Spells

Additional Spells

Antimagic Field

Appearance Altering Spells

Ab-Dalzim’s Horrid Wilting

Arms of Hadar

Blade Ward

Cantrips Improve with Level

Ceremony

Chain Lightning

Charm Person & Friends

Chill Touch

Conjure X

Contagion

Cordon of Arrows

Counterspell

Dispel Magic

Enthrall

Find Familiar

Find the Path

Healing Spirit

Immolation

Jump

Grasping Vine

Guidance

Lighting Arrow

Longstrider

Mordenkainen's Sword

Minor Illusion

Mirror Image

Ray of Enfeeblement

Resurrection

Simulacrum

Sleet Storm

Spare the Dying

Stoneskin

Time Stop

True Strike

Wall of Water

Witch Bolt

Equipment

Additional Equipment

Additional Weapons

Adventuring Gear

Disability Remedies

Expected Magic Items per Level

Greataxe

Healing Potions

Instrument of the Bards

Magic Item Crafting

Magic Item Properties: Temperate

Magic Item Prices

Minimum Damage

Poison DCs

Potion Consumption

Rituals

Shield Doffing

Silver Standard

Spears Are Polearms

Spell Components, Focus, & Item Interaction

Starting Gold

Strongholds

Swimming in Medium or Heavy Armor

Thrown Weapons

Tool Proficiencies Expanded

Vehicles and Ships

Gameplay

Action Options

Attack Spells targeting Magic Resistance

Buy-In from Players

Casting More than One Spell per Round

Casting Rituals while Moving

Climbing a Larger Creature

Dis/Advantage: -/+5 on Passive Checks

Downtime Activities

Running a Business

Building and Maintaining a Stronghold

Require Training to Gain a Level

Eliminate Bonus Actions

Falling Damage

Fleeting Luck

Followers

Fronts

Hero Points

Healing Surges

Hireling Morale

Holding Breath in Combat

Honor & Sanity, Fear & Horror

Initiative

Initiative Score

Side Initiative

NT's Initiative

No Initiative

When to roll initiative

Injuries

Inspiration: Session Statement

Inspiration: Additional Uses

Knocking a Creature Out

Level Drain

Level Gain Process

Miraculous Strike

Ranged Attacks Within Melee Reach

Monsters, Homebrewed

Mooks and Minions

Overland Travel

Paragon or Solo Monsters

Paralyzed Targets Can't Move

Plot Points

Readied Actions & Opportunity Attacks

Renown

Rests, Short

Rests, Long, after Short Rests

Rests, Long, Overland

Seafaring

Spell Points

Spellcasting Underwater

Surprise

Throwing a Creature

Treasure Parcels

Torch in Combat

Unseen Attacker

Urban & Wilderness Resources

Zero Hit Points

Unearthed Arcana

Unsolved or Unsolvable Problems

Armor Plays a Big Role

Can't Multi-subclass

Challenge Rating Sucks

Dis/Advantages Don't Stack

Damage Type Effects

Druid: Circle of Dreams

Extra Attacks from Different Classes don’t Stack

Fighter: Arcane Archer

Locations as Encounters

Lycanthropy and Vampirism

Metagaming

Monk: Way of the Kensei

Nets Kinda Suck

Paladin: Oath of Conquest

Rest, Daily

Rests, Long

Sorcerer: Shadow Magic

Unskilled Characters Easily Outperform Skilled Ones

Athletics (Strength)

Acrobatics (Dexterity)

Sleight of Hand (Dexterity)

Stealth (Dexterity)

Arcana (Intelligence)

History (Intelligence)

Investigation (Intelligence)

Nature (Intelligence)

Religion (Intelligence)

Animal Handling (Wisdom)

Insight (Wisdom)

Medicine (Wisdom)

Perception (Wisdom)

Survival (Wisdom)

Deception (Charisma)

Intimidation (Charisma)

Performance (Charisma)

Persuasion (Charisma)

Wizard: War Magic

House Rule Zero

The ampersand – dragon between the Dungeons and the Dragons is called Ampersandra the Additional.

More seriously, the very first rule of playing a game is to have fun. Otherwise, why play the game at all? To that end, it is very useful to have a session zero at the start of a campaign (and even intermittently, between chapters): a session in which you lay out how you're going to play.

Unless you're doing solo play, the DM takes a back seat here. While he or she usually "runs" the game, the DM's main job in session zero is to listen, and not swim against the tide. This doesn't mean be mute during the whole session, on the contrary, this is the best time to workshop some ideas. But listen, and steal the players' ideas!

Take a poll on the kind of game folks want to play. Use the questions on page 34 of the DMG, and add your own. Intrigue heavy or combat light games aren't fun for everyone, but some may lean heavily towards them. Is the theme gritty and realistic or high fantasy? Is the arc episodic or is there one big quest that the party is pursuing? Is the campaign rated PG or R? How comfortable are you with evil player characters, or player characters who work against each other? Do you need support characters (a healer of some kind is a necessity in most campaigns that see harm frequently befalling the PCs), or if you want an NPC support character in the party? Do you want to use a map and miniatures, or prefer to use the theatre of the mind?

At the risk of sounding self-serving, discuss optional house rules, maybe starting with these:

  • the ones I've highlighted in orange in this document

  • house rules that might be dear to a player (or DM)

  • some of the official options, such as whether you want to play with multiclassing or feats 

  • any special equipment characters might start with

  • how to generate ability scores

  • rule sources: is it core books only, anything goes, or are you using the Adventurers League "core (PHB) plus one other source book" rule? 

At risk of sounding really self-serving, play the game you want to play: RPG designers expect you to house rule things. So, you're playing wrong if you don't. 

Players should at least start to build out their characters, and talk about how they can weave their backgrounds together. Generally, each character should be able to somewhat trust at least one other character. Otherwise, it doesn't make sense for them to trust each other with their lives. You can do this randomly (roll a die to define which other character is each character's "trusted one") or by just picking out what makes sense. 

Discuss the setting and how the PCs fit into the world. While there's a lot the DM can say, but here, again, the players should take the lead in fleshing out this subject. Discuss each character's motivation for being on the adventure. It's important to make characters that are fun for everyone, not just one player. While there's lots of literature on how to be a good DM, but there isn't much on how to be a good player. Maybe talk about that a bit too: if you're reading this, it might not apply to you, but it probably applies to other players at the table.

Discuss logistics and etiquette: being on time, taking your turn, being ready on your turn, the schedule and how to RSVP, location and frequency of play, is booze acceptable, and so on. Consider calendar events and inviting everyone to them, especially when playing online in different time zones.

Make a note of the decisions made during session zero, and review them every six months or so. Some say it's best to review them briefly at the start of each session. See if the DM and the players are keeping to the expectations, or if the expectations have changed.

Alignment & Ability Scores

Against Rolling Ability Scores (and HP)

If players want to roll their ability scores, they must generate a random array of ability scores using the point-buy method or randomly pick an array among the legal possibilities. Players are not allowed to reroll ability scores or HP under any circumstance.

The problem with rolling ability scores with the traditional method is not so much the disparity in rolls, it's that reasonable DMs will treat players unfairly. If a player rolls low, any reasonable DM will allow a reroll of some kind, ignoring the fact that doing so dramatically changes averages and gives rerolling players much better odds of getting ability scores that are much higher than the average of characters made following the rules strictly. Statistically, even if those characters don't need a reroll because the first rolls were good enough, the average will be impacted by the mere possibility that the player could have rerolled the ability scores.

This consideration skews ability scores to much higher averages than legal characters. The summary of that link is that allowing the player to reroll their ability scores once is the average equivalent of 36 points if you're buying the ability scores (the normal allotment is 27 points), and being able to reroll your ability score set twice is the average equivalent of a 38 points worth of ability scores. The standard deviation also indicates that taking the best of any number of rerolls not only makes it more likely to get a higher average, but makes that much more reliably the case, as the standard deviation goes down by about one for each reroll. 

If I asked for 9 (or 11) extra points on my ability score point buy, any reasonable DM would respond with some colorful language. But the same DM would, quite reasonably, allow a player to reroll bad rolls, since playing a character with cripplingly low ability scores will dramatically impact the player's ability to enjoy the game.

This same issue applies to rolling hit points. Allowing a character that would be crippled by a terrible HP roll to reroll is absolutely reasonable. It's just completely unfair to other players' characters who have legally achieved numbers.

A hardass DM might read this and simply consider the option of being tough on rerolls and not allowing them: you roll one set and you keep it. This has a different bad consequence: good players will graciously agree, and play along with a character that's less fun to play, even if it's a melee character with a very small number of HP (for example). Since we play games to have fun, this seems like a bad solution.

Even the developers have noted that it's a good idea to take the suggested "average HP," although their absurd motivation is to avoid potentially losing HP when gaining a level.

If you insist on rolling ability scores, do it this way: use one set of rolls for everyone to arrange however they want to. That way, it's absolutely fair.

Alignment

Alignments are reserved for creatures from the outer planes and creatures tightly connected to them (such as, possibly, paladins and clerics). Otherwise, they are replaced by the following axis (score any or all on a 1-5 range, 5 indicating the latter extreme):

  • Ambition/Contentment

  • Bravery/Cowardice

  • Charity/Avarice

  • Chastity/Lust

  • Diligence/Sloth

  • Gregariousness/Shyness

  • Honesty/Deceit

  • Humility/Pride

  • Justness/Arbitrariness

  • Kindness/Envy

  • Patience/Wrath

  • Temperance/Gluttony

  • Zeal/Cynicism

Otherwise, alignments create strange and unrealistic behavioral limitations. Second part is taken from here.

Charisma: Previously Acquainted NPCs 

At character creation, PCs get a number of tokens equal to their Charisma SCORE. Subject to the DM's consent, and only if it is plausible, once per level they can trade in a token to declare that their character was somehow acquainted with an NPC they just met during the game.

This helps integrate PCs into the setting a bit more.

Dexterity: Not the Only Initiative Bonus

The highest among your Dex, Int or Wis bonus applies to initiative.

Otherwise, Dexterity is the most valuable ability score in the game, particularly for martial characters. I consider this change necessary along with the one below that benefits Strength. Spell casting can incentivize Wis, Int, and Cha, when present; and Con and Wisdom affect important saves against a great many spells and effects (poison, disease, and mind control, usually), concentration checks (important for casters) and hit points (important for martial characters, and generally everyone). But the system seems to significantly incentivize Dex martial characters over Str ones. 

To illustrate, here are all the Str benefits in the books:

  • Bonus to hit with melee weapons 

  • Bonus to damage with melee and thrown weapons

  • Str save against a few spells and effects (forced movement, usually)

  • Capacity to carry more weight

  • Bonus to Athletics skill checks

  • Multiclass classes allowed with Str 13

    • Barbarian

    • Fighter

    • Paladin (with Cha 13)

Dex benefits in the books:

  • Bonus to hit with ammunition and light weapons

  • Bonus to damage with ammunition and light weapons

  • Dex save against a great many spells and effects (area effect attacks or traps, usually)

  • Initiative bonus

  • AC bonus to no armor, light armor, and medium armor, although the latter caps at 2

  • Bonus to Stealth skill checks

  • Bonus to Acrobatics skill checks

  • Bonus to Sleight of Hand skill checks

  • Bonus to Thieves Tools proficiency checks

  • Bonus to Vehicles (Land) proficiency checks

  • Bonus to Vehicles (Water) proficiency checks

  • Bonus to Instrument proficiency checks

  • Bonus to some types of Artisan proficiency checks

  • Multiclass classes allowed with Dex 13:

    • Fighter

    • Monk (with Wis 13)

    • Ranger (with Wis 13)

    • Rogue (which grants Sneak Attack, of huge utility to most Dex martial characters).

Shifting Important Ability Scores

The racial bonus to an ability score can be moved to another ability score that does not have a racial bonus. Subject to DM approval, a spellcaster can use a different ability as their spellcasting ability.

This allows for charismatic wood elves and for Intelligence-based warlocks. New Dexterity or Wisdom based casters should probably be avoided, since those ability scores already have a big impact in the game. Also, allowing Strength to be a spellcasting ability feels wrong.

Strength: Additional Benefits

Add 1.5 times the Str bonus (rounded down) to damage for melee weapon attacks when wielding the weapon with two hands.

Str bonus applies to intimidation and some other social checks (somewhat overlaps with this fix).

The Str bonus is added to HP at first level.

Half the Str bonus, rounded down, applies as an AC bonus for heavy armor.

The Str bonus can be added to AC instead of the Dex bonus. The same armor limitations apply: max +2 for medium armor, no bonus for heavy armor. 

Str bonus can apply to AC instead of Dex (except at high levels for Barbarian), subject to the same limitations that armor weight imposes on the Dex bonus.

This is necessary to help make Strength a bit more useful in general, and to help it compete with Dex in combat for martial characters. More reasoning on this is under the houserule spreading the initiative bonus from Dexterity to other ability scores. Str Armor bonus suggested by Patrick O'Hagan.

Intelligence: Additional Proficiencies

For each odd positive Int bonus increment (+1, 3, 5 etc) you gain proficiency in a new skill, tool, or language at the corresponding level. For each such even increment (2, 4, 6 etc) you gain proficiency in a new tool or language at the corresponding level. Classes that use Intelligence to determine spell DCs or attack bonuses (of any kind, not just for spells), get one less additional proficiency.

Otherwise, Intelligence is not valuable enough. I'm not sure how to implement the latter limitation If you multiclass into an Int class late in a character's career, though…

Wis: Passive Perception is Check Floor

Perception checks can't be less than a character's Passive Perception.

Source: this interview at 15:30 and on (have not verified myself).

Races & Backgrounds

There are tons of homebrew race options, someone has even made playable races of all the monsters, but I'm not going to put together a comprehensive list or review. There is a respected guide for evaluating races here. Interested players and DMs should review them as well as the commentary on them, but keep an open mind to using them, since 5e is pretty forgiving towards homebrew projects.

Additional Backgrounds

If you need more backgrounds, some cool ones are here.

Alternative Background Feature

Backgrounds give you knowledge of a subject like so.

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Otherwise background abilities rarely see any use. The Hermit and the Sage, as presented here, are a bit problematic, so that knowledge should be fleshed out more with the DM.

Background Trinkets

Choose or roll a d100 for a random background trinket.

I'm not sure the trinkets that go with backgrounds are always appropriate, and if you build your own background, you should still get a trinket.

Changeling

Changelings can get +3 to Charisma by putting their floating modifier in the same ability score. 

Source.

If the changeling is playing a class that uses Charisma for their attack rolls (e.g. Hexblade, or Sorcerer) or makes other significant use of the ability score (if, for example, using the houserule allowing players to shift important class abilities to Charisma), then this may become a mild problem.

Otherwise, Charisma is not an ability score that already sees too many benefits (such as Dex might be, as suggested below), so this shouldn't be an issue. 

Beastfolk

Optional race I love found here, with a discussion about it here (prior version here). While the additional skill proficiency granted by Natural Talent might be abused by selecting stealth or perception proficiency, a background can also yield the same benefit, so it's not a real problem. 

Darkvision sees as if Dim Light

If you have Darkvision, treat darkness as dim light (disadvantage on perception checks involving sight and -5 to passive perception).

Source: the PHB, on page 23, under Elf Traits.

Darkvision only for Undergrounders

Replace Darkvision with low-light vision for all races that don’t live underground (or deep underwater). Creatures with low-light vision can see in areas of Dim light as if it were Bright light, and then 10' past areas of Dim light as if they were in Dim Light.

So Drow, Sniverfblin, and others who live permanently underground (or deep underwater) would keep darkvision, but elves, orcs, and other races who live above ground trade it for low-light vision. Suggested by me to increase drama and make darkness ominous and threatening. Andy feels okay about this. This also somewhat reflects the public's perception of which races should really have what kind of darkvision

Dragonborn: Subraces

The subraces noted here are used. 

Just extra options. This may not be compatible with the damage type additional effects listed below.

Dragonborn: Breath Weapon Effect

Receive the additional effects for their breath weapon listed in the Damage Type section.

This is to boost an otherwise slightly weak race. Another, perhaps better option, is to use the Intensified Dragon's Breath feat.

Secondary Backgrounds

Additional ways to tweak your backgrounds are here

Some extra options just for the sake of having them. Quite balanced, since they basically trade some features for similar features.

Variant Human 

Found in PHB Chapter 2, the race would gain an extra feat at character creation, instead of a variety of other benefits. They are often considered among the strongest choice of race, but I don't think they break the game, and have the advantage of returning it to its human-centric focus, while the "vanilla" human is certainly somewhat lackluster. Andy strongly endorses using the Variant Humie.

If the variant human is considered too strong or if you prefer not to use feats, there's an excellent alternative available here that serves that niche, with the main features being 2 and 1 ability score boosts, an extra advantage per short rest, and an additional proficiency and language.

If you'd like more variety among humans, here's a well-received human-only setting. I think it has 13 different human sub-races, so it should fit the bill, but I have never looked at it myself.

Warforged

The Eberron warforged is used.

This variant of warforged is used, but the Soldier Alternative Model's Shock and Awe feature is replaced with: 

Ready for Combat: You are always on guard, ready whenever combat breaks out. You gain a +2 bonus when rolling for Initiative.

The UA warforged playtest is considered rather boring (although it certainly does work), and this is the best alternative I've found so far.

Classes

As with races, there are a myriad of homebrew classes and subclasses, which I will not even attempt to comprehensively list or review here, other than noting that there's even a classless system that seems pretty balanced (you spend xp to gain access to features), and a pre-class commoner "class" in which you build up to finally getting a real class. However, folks should feel welcome to explore and discuss other options, since 5e is rather forgiving, but keep some wariness for multiclass builds.

Multiclassing

Found in PHB Chapter 6, it’s an optional rule that, like many others, I have no strong feelings about. If we don’t adopt it, under the rules, you can only take levels in the class you selected when you first created the character.

While most multiclass builds are generally inferior to straight builds due to losing out on Ability Score Increases (and capstone features), it should be noted that there are a few multiclass builds that are close to game-breaking, albeit not quite so. However, you table may feel differently. The builds in question (using the official classes) are Paladin and Warlock builds due to the extra spells that can be used to smite, Circle of the Moon Druid and Monk if unarmed attacks work for natural attacks, Assassin and Warlock using Darkness and Devil's Sight, Dex weapon users with Rogue to get Sneak Attack, combining Life domain Cleric and the Druid's Goodberry, Sorcerer and Warlock casting quickened Fireball + Eldritch Blast + Agonizing Blast is a bit much in one round, and there may be others I've missed. This is, in part, an issue that is due to lackluster capstones (addressed below for Bard, Druid, Monk, and Sorcerer), and the unlikelihood of achieving them during the normal course of play. While the latter doesn't have a clear fix, it may be worth moving the second Additional Save Proficiency, if used, to a level 20 feature of the starting class, to sweeten that achievement a bit (in addition to the capstone improvements suggested below). 

Additional Classes

In addition to the official WotC classes and subclasses offered in the Player's Handbook, the Sword Coast Adventurer's Guide and Xanathar's Guide to Everything, Eberron: Rising from the Last War, there are six more in the Adventures in Middle Earth Player's Guide. There is also a well reviewed Artificer class being developed here, or you can use the one in Eberron. 

I haven't reviewed the new books yet, but the designers and the studio publishing the MEPG is very respectable and trustworthy, and the Artificer has gone through a long revision process, which is some guarantee of playability.

Additional Save Proficiencies

At a character's 10th level, players choose a save their characters become proficient in. They select another save to become proficient in at level 15. 

Otherwise, a level 19 or 20 caster imposes a DC 18 spell saving throw. A level 20 target of such a spell who has a relevant ability bonus of, say, +1 and is not proficient in the relevant save will fail that save 80% of the time. The same issue applies to almost any save imposed by a monster of CR 15 or higher. This is problematic due to the existence of save-or-suck spells and effects like Charm Person or Feeblemind. The Resilient feat fixes this, if feats are used, by allowing folks to gain proficiency in the important saves (Dex, Con and Wis), but at the significant cost of one ability score increase and other customization. 

All classes have one good saving throw, and this fix gives them a second one at level 10. It's debatable whether a third one (the second italicized sentence above) is necessary, but given the availability of save-or-suck spells at high level, it probably is.

Barbarian: Path of the Brawler

This additional Primal Path is available. 

An option that I like.

Bard

Bard: Lore: Cutting Words

This feature can NOT undo a critical hit. This is here to note that, while Crawford (the designer of the game) once said that it could, he acknowledged his mistake here.

Bard: Magical Secrets

Can be retrained. 

Clarified by this sage advice. Otherwise considered a minor problem by MelloRed.

Bard: Superior Inspiration

The feature grants 2 uses of bardic inspiration if you have none when you roll initiative. 

Otherwise, the level 20 feature is pretty lackluster relative to other classes' capstones and encourages multiclassing. More discussion here.

Better Ranger & Druid Beasts

Level animals up or down, allowing Rangers to have a greater variety of level-appropriate companions, and Circle of the Moon Druids more wildshape options.

From this source. This is more necessary for the Beastmaster (more below), than the Druid, which is why there are two highlight colors. The Druid is only really problematic after level 9, at which point the only official wildshapes that are viable in combat are the T-rex and giant scorpion, which can only be used if the Druid has seen them. For something that is the central feature of a class, seems like the options are a bit scant.

Cleric: Discipline of Life

The feature applies to all healing spells, not just cleric ones.

As noted in this sage advice.

Cleric: Domains

Additional domains published in Xanathar's Guide to Everything published in Unearthed Arcana are available. 

Extra options just for the sake of having them. And now that they're in a real book, they're no longer that optional.

Druid

Druid: Archdruid

If you have no uses of wildshape left when you roll initiative, you recover one such use.

Otherwise, the level 20 feature for a Moon Druid (infinite healing) is too powerful relative to other classes' capstones and dramatically discourages multiclassing. More discussion here. The second part of the official feature (eschewing components when spellcasting) remains in place.

Druid: Circles

Additional circles published in the DM's Guild are available. 

This is a bit more necessary than the optional domains for the cleric because the Druid only has two subclasses, both of which are relatively complex. Adding a couple of options not only expands what is otherwise the class with the fewest character-building options, it also offers a mildly simpler version of the class for those who may be put off by all the details of the core druid subclasses. Not quite necessary enough to make it orange, though.

Druid: Wildshaped Dragonborn

Wildshaped dragonborn have access to their breath weapon. 

According to this sage advice.

Engineer

A well-reviewed and -revised homebrew I like a lot. Available here. Per Andy's suggestion, the scattergun has a cone-shaped area of effect, like a shotgun, but does half damage at long range.

Fighter

The Fighter benefits from some of the improvements suggested in the Unearthed Arcana article on Class Feature Variants.

Fighter: Action Surge

 Action Surge gives you an extra action, not an extra

bonus action. (Recent printings of the Player’s Handbook

no longer include the wording that provoked this question.) 

This is just a clarification on how this feature works. Copied from Sage AdviceCompendium

Fighter: Arcane Archer: Arcane Shot

The feature doesn't require a magical arrow.

Errata from Jeremy Crawford from before XGtE was even released.

Fighter: Arcane Archer: Arcane Shot: Curved Shot

Curved Shot doesn't end Magic Arrow

This is only necessary, since, under RAW, the latter ends when it misses a target. This is only an issue if an Arcane Archer isn't using a magic bow or arrow, missed their first target, and used Curved Shot to try to hit a target that has resistance or immunity to non-magical attacks.

Fighter: Champion – Hit Dice

For healing purposes, your hit dice are d12. But the hit points you gain at each level are still determined by a d10.

Or some other kind of buff. The expanded crit range at high level just doesn't add enough, particularly for those who want a simple sword & board or archery. Otherwise too weak and considered a minor problem by MelloRed.

Fighter: Eldritch Knight – Spell Components

You can perform the somatic and material components of spells even when both the character's hands are used to hold weapons or a shield. 

Otherwise can’t cast somatic spells while weapons or a shield (or two shields, if that is a thing) occupy both hands. This solution slightly erodes the utility of the Warcaster feat, since it wholly reproduces one of the feat's three benefits. This issue is perhaps better dealt with by an even broader houserule suggested below, but is definitely necessary for this archetype to be a viable one. 

The other reason this is highlighted orange is that, in addition to the above, the class is a bit fiddly overall. War Magic is only useful for a few levels (after which the extra attacks make the class rarely inclined to cast spells instead of attacking), the class depends highly on both an weapon attack ability score and the ability score controlling spell DCs, and there are several spell levels in which the class has few good choices. So, keeping casting as viable as possible becomes a bigger issue for this class.

Fighter: Eldritch Knight – War Magic

The intent is that the bonus attack can come before or after the cantrip. You choose when to take a bonus action during your turn, unless the bonus action specifies when it must take place (PH, 189). 

This is just a clarification on how this feature works. Copied from Sage Advice of June 2016

Fighting Style

Fighting styles are a feature available to many classes, including Fighter, Ranger and Paladin.

Fighting Style: Great Weapon Fighting

When you roll a 1 or 2 on a damage die for an attack you make with a melee weapon that you are wielding with two hands, you can reroll the die until the new roll is not a 1 or a 2. The weapon must have the two-handed or versatile property for you to gain this benefit.

Otherwise the reroll is worth less than a straight +1 to damage, as noted by this math. By way of comparison, the Dueling Style, a competing fighting style, grants a simple +2 to damage rolls with a one handed melee weapon, which makes it flat-out a better choice. It should be noted that boosting two handed weapons' damage might have a greater impact on the game, and it's probably fine to leave this as it is in the book. The latter link goes to the fighter features which lists the most Fighting Styles, but several classes have the Fighting Style feature.

This appears to have been my mistake. It's here until I review it properly, but deprecated.

Fighting Style: Dueling

The damage bonus applies to thrown melee weapons.

This is a clarification from sage advice.

Monk

The Monk benefits from some of the improvements suggested in the Unearthed Arcana article on Class Feature Variants.

Monk: Perfect Self

If you have fewer than 4 Ki when you roll initiative, you gain additional Ki to bring your Ki reserve up to 4. 

Otherwise, the level 20 feature is pretty lackluster relative to other classes' capstones and encourages multiclassing. More discussion here. The official rule also encourages randomly using Ki to bring it down to zero if one has less than 4, which is annoying.

Monk: Way of the Four Elements

This version of the subclass is used. 

Comments on an older version are here and here. Otherwise, the PHB version is weak and needs boosting. As an alternative, if feats are used, two extra ability score increases (like the fighter) might do the trick. Or, increasing the number of Ki points by the monk's Wisdom modifier (probably the simplest). Or, discounting their ki ability costs by one. 

Paladin: Oaths

Two additional well-respected paladin subclasses are reviewed here. Commentary in link.

Ranger

Either use consensus Ranger (a homebrew hybrid between the official Ranger and the Ranger published in UA) or replace Primeval Awareness with extra "domain" spells below. Maybe even the Alternate Ranger.

Otherwise considered a problem by MelloRed and the community in general. Even the WotC have tried one fix, but it's widely regarded as terrible. A good, almost final version official fix was published in this Unearthed Arcana, but it has a problem with multiclassing (dipping into Beastmaster Ranger for 1 or 3 levels is really good), and is still not considered that great of fix. On the other hand, the Ranger benefits from some of the improvements suggested in the Unearthed Arcana article on Class Feature Variants. I have not reviewed the Alternate Ranger, but I've heard good things about it, and it's been worked on very hard.

Some of the more common or legitimate complaints of the PHB Ranger are:

  • No combat features at level 1: considering that every other class has some kind of combat feature at first level, this seems weird and unfair.

  • Too many features of trivial use: the class has a lot of non-combat features that they only apply rarely in normal gameplay or have relatively little impact.

  • Has a similar level of spellcasting ability as paladins have, but they can only access a handful of the spells on their spell list, while the paladin gains access to their full list as soon as they can cast it.

  • Survivalist features duplicate Outlander background: not wholly, but much of the better features that allow the Ranger to shine during survival adventures are also available by taking some background elements. It's worth noting that, under the rules, backgrounds can be broken down and rebuilt piecemeal, so you don't even have to take all of that background to get the features that matter to you.

  • Vanish, a level 14 feature that allows you to use your bonus action to hide and cannot be tracked by non-magical means, is a worse version of the Rogue's level 2 ability.

  • Boring capstone feature: while a +5 (assuming max Wisdom) to hit or damage once per turn is nice, it isn't exciting. The paladin, by way of contrast, turns into a freakin' angel. This illustrates how rangers compare poorly with other classes at high-level.

  • Boring Beastmaster: when people envision a "Beastmaster," they envision trainer and beast fighting side-by-side. What Wizards gave them was the ability to have the Ranger or beast attack, but the beast can't use their usual multiattack until the Ranger gets to level 11. Further, the beast has bad saves and can easily die. Combine this with the fact that a lot of exotic creatures are unavailable and you have some unhappy folks. The problem here is that if the Ranger and beast could attack in the same turn at level 3 it would be ridiculous. Wizards opted for the balanced approach, but most don't like it.

  • Not kick-ass: the class went from one of the most powerful ones to a straightforward, balanced one. Some of the criticism is undeserved: a Hunter with Hunter's Mark and Swift Quiver can be quite strong in battle. But the contrast remains: an archery Fighter will outshoot an archery Ranger, and melee is worse.

Ranger: Beastmaster

Give beast hit dice. Ranger gains Revivify Beast spell. And add the following spells as known at the noted levels:

3: Animal Friendship, Speak with Animals.

5: Revivify Beast (see below), Warding Bond.

9: Conjure Animals, Protection from Energy

13: Stone Skin, Dominate Beast

17: Rary’s Telepathic Bond, Awaken

Revivify Beast (Level 2 spell, ritual)

1 action: touch

Component: A body part of the creature.  

If a beast died in the last minute, it comes back to life with 1 HP

At higher level: At level 3, the beast could have died in the past day.  At level 4, the beasts regenerates missing body parts.  At level 5, you don't need the beast's body, it regenerates from thin air.

Otherwise Beastmasters are somewhat weak and are considered a moderate problem by MelloRed. Two problems with this solution: Rangers don't have a wizard-like (or any) ritualist feature. And, practically, the Ranger would have to keep this spell prepared at levels 5-8 to be able to use it, occupying a precious spell slot all the time. Maybe make it level 1? Or give Beastmasters a Wizard-like ritualist feature so that they can cast it even if they don't have it prepared.

An alternative is to import the similar well-reviewed suggestions here.

Ranger: Hunter

Add the following spells as known at the noted levels. 

3: Hunter's Mark, Primeval Awareness (as a level 1 ranger ability).

5: Pass without a Trace, Locate Animal or Plants

9: Nondetect, Water Walk

13: Freedom of Movement, Locate Creature

17:Tree Stride, Scrying.

Otherwise considered too weak and a minor problem by MelloRed.

Ranger: Hunter: Horde Breaker

A 5th level Hunter Ranger, with the crossbow expert feat, can pull off 4 attacks in a turn (by using both their action and their bonus action), if two of the targets that are within 5' of each other.

Clarification provided by this Sage Advice.

Ranger: No Spellcasting Focus

Rangers may only use a component pouch in place of cheap spell components, and may not use any other spellcasting focus.

Simply based on the fact that the Ranger has no entry for a Spellcasting Focus..

Rogue

Rogue: Reliable Talent

This feature is triggered by even a half-proficiency bonus, such as with Remarkable Athlete. 

This is an odd clarification by the game designers. Source is this sage advice.

Rogue: Sneak Attack

The Rogue is expected to get Sneak Attack every round. 

As noted here and here by the game designers.

Rogue: Swashbuckler: Rakish Audacity

Swashbucklers don't get sneak attack when they have disadvantage, even if they meet the other Rakish Audacity requirements. 

This is a clarification contained in this tweet that states that it will be published in Xanathar's Guide to Everything.

Starting Gold

Players who elect to take starting gold instead of the equipment offered by their class use the dice described towards the end of this article, which is reproduced here:

Class

Starting Gold

Artificer

5d4 x 10 gp

Barbarian

3d4 x 10 gp

Bard

4d4 x 10 gp

Cleric

5d4 x 10 gp

Druid

3d4 x 10 gp

Fighter

8d4 x 10 gp

Monk

1d4 x 10 gp

Paladin

8d4 x 10 gp

Ranger

4d4 x 10 gp

Rogue

3d4 x 10 gp

Sorcerer

2d4 x 10 gp

Warlock

4d4 x 10 gp

Wizard

4d4 x 10 gp

 

The article explains this in detail, but otherwise the gold rolled for any class except the artificer, cleric, warlock, and wizard would almost never be enough to purchase the standard equipment for that class. 

Sorcerer

The Sorcerer benefits from some of the improvements suggested in the Unearthed Arcana article on Class Feature Variants.

Optionally, this version of the class is used.

It's pretty nice, and has about 10 subclasses.

Sorcerer: Favored Soul

If this subclass is used, the UA 2/6/2017 version is used.

Prior versions of this class were too powerful. Multiclassing into this class still remains pretty powerful.

Sorcerer: Quickened Metamagic

You can't cast a bonus-action spell if you cast a non-cantrip spell or invocation during your regular action on the same round: if you cast a bonus action spell and want to cast another spell in the same round, the normal action spell must be a cantrip. You can, however, cast any reaction spell along with any other spell, as long as you comply with the prior sentence. Somatic, verbal and material component restrictions still apply, and usually make casting more than one spell at a time impossible.

This first sentence clarifies what is already in the rules, on page 202 of the Player's Handbook, under the Casting Time: Bonus Action. The second sentence clarifies that the first doesn't restrict anything more than casting bonus-action spells. The third sentence points out that component rules still apply. Unless two spells have completely independent component requirements (e.g. one is only verbal and the other only material and somatic), you won't be able to cast them at the same time.

Sorcerer: Sorcerous Restoration

Recover 6 expended sorcery points every short rest.  Recover 4 expended sorcery points if you have fewer and initiative is rolled.

Otherwise, the level 20 feature is pretty lackluster relative to other classes' capstones and encourages multiclassing. More discussion here.

Sorcerer: Wild Magic

If the Wild Magic sorcerous origin is considered undesirable, the Raw Magic origin can be used instead.

Self explanatory. The link contains a variety of sorcerous origins.

Warlock

The Warlock benefits from some of the improvements suggested in the Unearthed Arcana article on Class Feature Variants.

Warlock: Pact Blade

The Warlock can use Cha for melee attacks with the pact weapon. 

Otherwise Warlocks need to pump Str or Dex in addition to their class ability to be effective. The problem with this solution is that it treads on the toes of the Hexblade, from XGtE, who enjoys this suggestion as a feature. Considered a moderate problem by MelloRed.

Warlock Patron: The Machine

This additional Patron is available as a Warlock subclass. 

Simply appeals to me.

Wizard: Illusory Reality & Minor Conjuration

Cannot be used for material components. 

Otherwise too powerful and considered a big problem by MelloRed.

Feats 

Found in PHB Chapter 6, are something I and Andy feel strongly about, in positive, warm ways. Feats allow a character to trade in their ability score increase to gain a feat instead, and, after class and race (and couple of choices within a class), are one of the very few ways of making a character unique. Lane is opposed to feats.

Additional Feats

Additional feats published in UA are available. Dragonborn might use the additional feats available here. More are available in the Wilderness & City Guide.

They simply make the game a bit more interesting.

Feat Point Purchase System

Feats are paid for with points as described here, but using these costs.

Feats have a very disparate impact on gameplay, and some feats are much more useful than others. This helps account for that, and allows the selection of "lesser" feats by paying fewer points.

This alternative, while better overall, is deprecated because it departs too radically from the 5e game (and dramatically approaches the second edition of Pathfinder).

Charger

Deal extra damage equal to 2x your proficiency. 

Otherwise not enough benefit and considered a moderate problem by MelloRed.

Crossbow Expert

The damage of the bonus action attack does not get any ability score bonus added to it, should it hit.

I’m not sure if this enough or too much, but there's no other clear way to nerf it without making it too weak, according to MelloRed. 

Elemental Adept

Reroll 1's on damage rolls of chosen damage type. Use the new result, even if it is a 1. 

Otherwise considered too weak and a minor problem by MelloRed. However, this math says the feat is fine, so it might be worth leaving it as written.

Grappler

Can grapple creatures 2 sizes larger. 

Otherwise the first existing benefit is just a variant of the shove-to-prone combat option grapplers already have, and although it avoids the need of an attack action to obtain advantage on attacks, it denies that benefit to others. The second existing benefit imposes restrained, which means the target suffers from disadvantage to all Dexterity saving throws: this works nicely with grapplers who use Dexterity-based spell damage or allies attacking the same target, but is rarely of benefit to the grappler, who already has advantage on attacks thanks to the first benefit. The third existing benefit is completely worthless (as explained in this sage advice and PHB errata), and has even been removed from the website

If this is implemented, The "price" of this feat in the 

Great Weapon Master

-3 to hit, +d12 damage. 

Otherwise considered too much damage and a moderate problem by MelloRed. The need for this fix is also illustrated by the fact that any reasonable high-damage build using either Great Weapon Master or Sharpshooter dramatically outpace other builds. The more common fix proposed is to subtract proficiency bonus from the attack roll and add double the bonus to the damage, but that has other problems.

Intensified Dragon's Breath

This optional feat is available to Dragonborn.

It's a fun feat, and keeps their breath weapon useful at higher levels.

Jack of All Trades

Applies to all ability checks, including initiative rolls and spells like Counterspell.

Per PHB page 54 and page 174, under Ability Checks.

Lucky

When used on a roll with disadvantage, this feat allows a player to pick the best of three d20. You are still considered to have disadvantage, so a feature like Sneak Attack is blocked.

These are two clarifications by sage advice. This might be the most potent feat in the book, and might need nerfing, although this reading is most in line with the meaning of the word "lucky." Crawfod, the game's lead designer, houseruled the feat in the way it was clearly intended to be played (first deal with disadvantage, and then pick between that result and the "lucky" roll). If you're interested in it, here's some data about how the two different rules play out.

Martial Adept

Grants 2 dice. 

Otherwise considered not worthwhile, and therefore a moderate problem by MelloRed.

Medium Armor Mastery

+1 AC, no penalty to stealth. 

So 12 – 14 Dex people see a benefit. Otherwise considered not worthwhile, and therefore a minor problem by MelloRed.

Polearm Master

Make the Opportunity Attack with the polearm. 

The game designers have already said this was the intent. This could almost be considered a clarification. Otherwise considered a big problem by MelloRed because it grants the ability to make opportunity attacks in other ways, which can lead to strange builds exploiting this loophole. 

It should be noted that you can still cast Booming Blade or Green Flame Blade as an opportunity attack with the War Caster feat, even if the opportunity attack was triggered by this feat, as long as you use the polearm to make those spell attacks. Further, to make those attacks at 10' of range with a polearm, the Spell Sniper feat is necessary. Also, while Green Flame Blade affects more than one creature, it only talks about one target, which makes it work for opportunity attacks with War Caster.

If you're comparing Polearm Master to Great Weapon Master, here's some good data to help pick which one you should use first.

Savage Attacker

Either +1 Str or +1 Dex. Also, reroll the damage on one weapon or unarmed attack per turn, using either result

Otherwise not worthwhile, and therefore considered a moderate problem by MelloRed.

Savant (New Feat)

You may not be smart, but you have your moments. You gain the following benefits:

  • Prerequisite: pick a skill related to an ability score in which you a negative modifier.

  • Replace the ability score modifier for just that skill with +4.

Otherwise ability scores are almost always the main modifier to a skill, and players are deterred from investing in that skill even though it would make sense for the character. Inspired by this post.

Sharpshooter

-3 to hit,  +d12 damage. 

Otherwise too much damage benefit, and therefore a moderate problem by MelloRed. The need for this fix is also illustrated by the fact that almost every high-damage character build using either Great Weapon Master or Sharpshooter dramatically outpaces other builds. The more common fix proposed is to subtract proficiency bonus from the attack roll and add double the bonus to the damage, but that has other problems.

Shield Mastery

Take the bonus action before or after any of the attacks of your attack action. 

Jeremy Crawford (the game's designer) uses this, and has used the part that is stricken above. This house-rule is a bit more fun.


Spells

A good summary of all the spellcasting rules is here. Here is a listing of 5e spells. Many spells are simply underpowered, but I don't want to change their level, since players wouldn't look up the spell before they have access to it. Also, while most low level fixes are rated green, high level casters only have a small handful of slots for spells of level 6 or higher, so the suggested changes to spells of that level and that sound good even though they are not (i.e. traps for inexperienced players) are rated yellow.

A good source to review the relative utility of spells is Treatmonk's ratings.

Additional Spells 

The spells in the  (Not Quite) Complete Tome of Spells (pdf is here) are available. Additionally, the spells in Metabot's Manual of Magical Martial Maneuvers are available. And, finally, some non-adventuring spells in Mundane Magic

Without the first and second sets of additional spells, some builds seem to be rather light on spell choices.This particularly affects light casters (for example, those taking the Ritualist feat, Eldritch Knights and Arcane Tricksters). But even the moderate casters (Rangers and Paladins) seem to hit some levels where there are very few good choices. Further, even full casters have some levels that only offer lackluster choices: as far as level 9 spell choices go, Clerics can generally only choose between Mass Heal and Gate, and the latter is very DM-specific. Many clerics will use their 9th level slot to cast a lower level spell, such as Spirit Guardians at the highest level. The other two 9th level Cleric spells (Astral Projection and True Resurrection) are only useful in relatively specific circumstances. This becomes more urgent if the optional multiclassing or feats rules are not used, since players are more restricted to the spells of their original class. 

While the Sword Coast Adventurer's Guide and Xanathar's Guide to Everything added some spells, these additions aren't really sufficient to address the issue. For example, in XGtE, Eldritch Knights only gained 14 new spells (3 of each level and two new cantrips). And SCAG only added a total of 4 new cantrips.

Not all the options in the (Not Really) Complete Tome of Spells are perfectly balanced, but as the very existence of this section demonstrates, neither are the official options. However, Gemidan's Paralytic Missile is way too powerful as a cantrip, because any melee hit on a paralyzed target is a critical hit. On the other hand, Fireblast and Comet Strike may be a bit too weak in their effect. I am not going to review all the options in the book, so please understand that not all spells are worth taking or allowing in a game. Nonetheless, the publication does add a lot of options for spellcasters, which is the goal here.

The spells in Metabot's Manual are a little more helpful for half-casters, since many of them involve melee attacks, which are useful to half-casters. Since half-casters are the ones with the least good official choices, this is worth using.

The spells in Mundane Magic seem to be the most necessary of the bunch for a setting in which magic exists, even though they will have very little impact on actual gameplay. 

Most classes benefit from the additional (albeit not new) spells they have access to if you use the suggestions in the Unearthed Arcana article on Class Feature Variants.

Antimagic Field

Antimagic Field also affects Monks' Ki powers.

According to Jeremy Crawford's tweet. Given how powerful the spell is, I don't really see a good reason to rule this way, but he's the game designer, so I'm assuming that's correct. This might also be the simpler way to do things, which is a virtue in a relatively complicated game.

Appearance Altering Spells

Disguise Self – 1st Level – 1 Hour – You as well as your belongings look different. 1' shorter or taller, thinner or fatter, but must use the same body shape (can't turn a human into a spider for example). Doesn't hold up to physical inspection.

Alter Self – 2nd level – 1 Hour – Basic shape can't change but you become that form. It is a transmutation rather than an illusion like Disguise Self.

Seeming – 5th Level – 8 Hours – Can change the appearance of any number of creatures including unwilling creatures pending a CHA save. Appearance is same rules as Disguise Self.

Shapechange – 9th level – 1 Hour – You assume the form of a different creature of CR equal to your level or lower (except construct or undead). You become that creature but keep your alignment and mental scores. Essentially a crazy good version of Wild Shape. Inspection would show you as the creature you are but Truesight would see the true form.

Polymorph – 4th Level – 1 Hour – Same as Shapechange except you don't retain your mental scores. You also are limited in what you can change to only beasts.

Just a convenient summary.

Ab-Dalzim’s Horrid Wilting

The errata version (doing 12d8 necrotic damage) is used.

Fixed in Elemental Evil Companion errata. Otherwise, this spell is worse than fireball in almost every circumstance, and of higher level than fireball. The rare exception is if you’re in command of a horde of undead, who are immune to the spell, which means you can use the spell without fear of injuring your undead. 

Arms of Hadar

Caster can select targets, and a successful save halves damage.

Otherwise, bad due to friendly fire, requiring the caster to go into melee, and targeting a save that is often very good,. 

Blade Ward

Also gain temporary Hit Points equal to your level for the duration of the spell.  

Otherwise, despite halving damage, most of the time, simply dodging is better, because dodging gives disadvantage to all attacks targeting you and advantage on Dex saves until the beginning of your next round, and Blade Ward simply halves all incoming weapon damage. The two effects are comparable, but Blade Ward displaces some other cantrip that could be much more useful, while Dodge is always available to everyone. 

Cantrips Improve with Level

All cantrips improve as described here

Otherwise, non-attack cantrips don't really increase in effectiveness, and a 20th level Wizard's light spell is the same as a 1st level Wizard's. There's a reddit discussion thread about the improvements here.

Ceremony

If this UA spell is used, the following text is added to the "Marriage" portion:

As long as all the humanoids were bonded with marriage for the first time and all of them feel true love for each other, they gain these benefits while located on the same plane of the existence:

  • They can sense the direction and approximate distance of each other.

  • They can feel intense emotions of each other such as pain, grief or rage at any distance.

  • They can feel all emotions of each other when within 30 feet of each other.

Too good a reference to miss.  

Chain Lightning

The caster can affect any creatures he or she chooses in a 50' sphere. 

At higher levels: increase sphere diameter by 10' and damage by 1d8 per level above 6th.

Otherwise worse than Fireball in almost every way, even though it's three levels higher.

Charm Person & Friends

If the target failed its first save, when the spell ends, it has to make another save to realize that it was under the effect of the spell. If it makes that second save it becomes hostile, as described in the original rules. If it fails that second save, it's merely confused about what happened.

Otherwise, the spell's utility is so limited that it might as well just be a "open lock when the person with the key is around" spell. If this is deemed too powerful, one could add the following limitation: 

The target may not have been targeted by this spell in the past 24 hours.  

Chill Touch

The spell is renamed "Spectral Blast."

The spell doesn't require touch and does no cold damage. The original name is confusing AF.

Conjure X

Creatures do not have any 1/day spells or spell-like effects. 

Not necessarily the best fix. Otherwise considered a big problem by MelloRed. For example, without this house rule, druids are exceptional healers because they can conjure creatures that have healing spells. Sage Advice says these creatures are chosen and controlled by the DM, so maybe they wouldn’t cast all their spells But this remains problematic, since conjurations will fight to the death, so it's confusing as to why they wouldn't cast all their spells.

Just to provide some extra context, here's a Guide on 5e Conjurations.

Contagion

Disadvantage on Con saves due to Slimy Doom does not apply to the saves required by this spell. Contagion takes 3 failed saves to kick in.

The part that's stricken through is to nerf what might be too potent a spell, according to MelloRed, but the second sentence is a Sage Advice clarification of the onset time. This doesn't address why contagion does not spread, which seems like a missed opportunity…

Cordon of Arrows

The damage is d6+2 per piece of ammunition. 

Otherwise, it's a bit weak. 

Counterspell

It takes a reaction to try to identify a spell while it's being cast, and that same reaction then cannot be used to cast Counterspell. Someone other than the Counterspell caster can use their reaction to identify the spell, and 

A clarification from Jeremy Crawford, the lead designer of the game. I don't love this notion because getting players to waste resources for no real reason doesn't really fit my notion of "fun," but tables vary on this issue. Obviously, another character can use their reaction to try to identify the spell and warn the Counterspell caster of what it is, but other characters might have other things to do with their reactions, leaving the caster to guess from the greater context as to whether this is a good spell to counter.

Dispel Magic

If a check is necessary, at higher levels, you gain +1 on the check for each level of the spell slot used above 3. 

Otherwise, casting the spell at higher level, unless high enough to automatically dispel, has no benefit. 

Enthrall

Duration: as long as the caster is stationary and keeps talking. Add concentration requirement.

Unless the target is hostile, or there is some threat of harm to them, the Wisdom save is with disadvantage. A new save can be attempted every few minutes, or if there is some threat of harm to the target.

Otherwise too weak for a 2nd level spell: short duration and too likely to fail (since the targets get to make a Wisdom save and a Perception check (albeit with disadvantage). 

Find Familiar

Remove owl from the list of potential familiars. 

Otherwise the caster has a flying scout that has high stealth and darkvision, and can deliver touch attack spells while avoiding opportunity attacks with Flyby. All of this makes it much more powerful than all the other options, and overpowered for the spell level. The alternative would be to rewrite the owl, which seems unnecessarily complicated. Billy Coz thinks that removing the Flyby feature would make it okay.

Find the Path

Duration: instantaneous. The caster gains knowledge of the distance and the shortest route to the location. Add "Ritual" tag.

Otherwise too weak for a 6th level spell, for which casters have very few slots. Probably needs further improvement.

Healing Spirit

The spell ends once the spirit has restored hit points a number of times equal to 1+casting mod (min twice).

… equal to twice your spellcasting ability modifier (minimum of once). 

Remove concentration, add reaction to enjoy healing benefit.

Otherwise the spell can heal a very large number of HP during a short rest. The first deprecated house rule was actually suggested by Jeremy Crawford, one of the game's lead designers, who also has an upcoming errata for the spell, among other things, the leak of which is the main option now. The second deprecated option is suggested on D&D Beyond, and is just as valid an alternative.

Immolation

Doesn't automatically kill you at 0 HP but does 8d8 and then 4d8 fire damage.

Fixed in Elemental Evil Companion errata. Otherwise weak.

Jump

Duration: 1 hour.

Otherwise too situational to ever prepare.

Grasping Vine

The target of the vine's grasp is restrained until the caster's next turn.

Otherwise too weak: is two levels above gust of wind, but does almost the same thing..

Guidance

Casting time: reaction. Caster must succeed on a Wisdom save against a DC equal to ten plus the target's skill bonus to bestow the spell’s benefits retroactively after an ally has failed a skill check. 

Otherwise annoying to administer. This may still be too powerful a cantrip, even after this nerf. Beyond link.

Lighting Arrow

Each creature within 10' of the target (including the target) takes 2d8.  

Just to clarify it. Otherwise considered a minor problem by MelloRed.

Longstrider

Duration: 8 hours. 

Otherwise nobody will prepare it other than in corner cases.

Mordenkainen's Sword

Duration: 8 hours. 

Otherwise considered too weak and a moderate problem by MelloRed.

Minor Illusion

An illusory object created by a minor illusion doesn’t move.

This is just a clarification from Sage Advice of June 2016. It remains problematic to the extent that everything is in motion and nothing is absolutely still, so I'm guessing this means it remains in a position that's constant relative to the significant objects that it is on or in or around. Or, relative to the ground, if it is neither on nor in nor around anything. 

Mirror Image

The AC is your normal AC (with armor and protective equipment) lowered by 2. 

Otherwise the AC is way lower than yours, so it is very likely you will lose all 3 images to attacks that would have missed anyway, making the spell almost useless.

Ray of Enfeeblement

Remove concentration requirement. Affects the attacks of creatures making Strength or weapon-based attacks. 

Otherwise it's too weak because it requires both an attack roll and a save, and only applies to a very narrow range of attacks (Strength AND weapon based attacks).

Resurrection

Matt Mercer's resurrection rule is adopted:

Character death can often prove to become a minor inconvenience in some campaigns once the adventuring party reaches a certain level, with spells being available to return fallen comrades from the afterlife with temporary setbacks, robbing a small element of danger, and threat to future conflicts and challenges within the story. If you wish to elevate the gravity of character death, you can introduce this optional rule.

If a character is dead, and a resurrection is attempted by a spell or spell effect with longer than a 1 action casting time, a Resurrection Challenge is initiated. Up to 3 members of the adventuring party can offer to contribute to the ritual via a Contribution Skill Check. The DM asks them each to make a skill check based on their form of contribution, with the DC of the check adjusting to how helpful/impactful the DM feels the contribution would be.

For example, praying to the god of the devout, fallen character may require an Intelligence (Religion) check at an easy to medium difficulty, where loudly demanding the soul of the fallen to return from the aether may require a Charisma (Intimidation) check at a very hard or nearly impossible difficulty. Advantage and disadvantage can apply here based on how perfect, or off base, the contribution offered is.

After all contributions are completed, the DM then rolls a single, final Resurrection success check with no modifier. The base DC for the final resurrection check is 10, increasing by 1 for each previous successful resurrection the character has undergone (signifying the slow erosion of the soul’s connection to this world). For each successful contribution skill check, this DC is decreased by 3, whereas each failed contribution skill check increases the DC by 1.

Upon a successful resurrection check, the player’s soul (should it be willing) will be returned to the body, and the ritual succeeded. On a failed check, the soul does not return and the character is lost.

Otherwise, when resurrection spells become freely available, they trivialize the penalty that death should be.

Simulacrum

Simulacra cannot cast simulacrum, wish, or regain hit points outside the lab.  

Otherwise too powerful. Other possible fixes: can't cast level 7+ spells? Or change wish to not remove costs? Otherwise considered broken by MelloRed.

Sleet Storm

Creatures in the area take 1 point of cold damage each round. Make one Constitution save against the spell to avoid this damage and to maintain any concentration spells.

At higher levels: add d6 damage per slot level above 3rd (save halves).

Otherwise too weak. Grease, two levels lower, has almost the same effect, although it's a smaller area, no obscuration, and no difficulty maintaining concentration spells.

Spare the Dying

Unless the body of the target has been completely destroyed, the target does not die due to events that occurred this past round. Likewise, any death saves failed during the last round are "unfailed" and the creature becomes stable. The target's condition is not improved in any other way.

This spell is removed from every spell list. 

Otherwise, this cleric cantrip is useless: it has the same effect as spending one Healer's Kit use (5 sp per use), or of making a DC 10 Wisdom (Medicine) check, and consumes a precious resource: occupying one of a small number of cantrip slots. Needs to do something better (like save a life, per palendromemoredenlap's suggestion) or be removed.

Stoneskin

This spell requires no concentration, and duration is shortened to 10 minutes. If cast as 5th level, extend duration to 24 hours or until the end of the character's next long rest, but require 5000 gp of diamond dust. If cast as 6th level, add resistance to magical versions of same damage, extend duration to a week, but require 400,000 gp of diamond dust.

Otherwise, this 4th level spell requires concentration and 100 gp of diamond dust for mere one hour resistance to nonmagical bludgeoning, piercing, and slashing damage. It seems not worthwhile, since most monsters encountered at level 7 or shortly thereafter have either magic weapons or do other kinds of damage, and concentration makes it compete with many other combat spells, so of limited use. 

For the higher level versions, those prices probably need some review or testing.

Time Stop

Can also cast spells on allies.

Otherwise probably too limited for 9th level spell.

True Strike

Casting time: reaction. Trigger: ?. 

Casting time: bonus action. Until your next turn, you may not use your reaction. 

The next weapon or cantrip attack you make is made with advantage. If it hits, it is a critical hit.

The target's next attack gains a bonus to attack equal to +1 and to damage equal to d6 plus the caster's spellcasting ability score bonus if the attack hits. The spell is wasted if the attack misses. This damage increases by 1d6 when you reach 5th level (2d6), 11th level (3d6), and 17th level (4d6). 

In the alternative, make the spell's effects last until the end of the turn after the target's next turn (two turns).

In either case, remove Concentration requirement. 

While the original version of the spell allows you to attack only on the next turn with advantage, this is, in almost every case, worse than attacking twice (once this turn, once next turn) since the latter has the same odds of hitting at least once, and the potential to cause more damage. Therefore, the original version of the spell would rarely see use. This spell becomes too potent if casting time is a bonus action, or a reaction, or even both. In all those cases, it becomes the default action to cast unless there is a reason not to. The bonus action casting time has the advantage of restricting other spells that can be cast on the same round to cantrips, which works well, but still makes it so potent that it would become a spell that gets used every time unless there is a reason not to.

The damage increasing solution allows the caster to use a divination spell to help someone's next attack without losing their contribution to the fight. The only real cost with this solution is that it delays the attack, but that's the smallest price I could come up with. According to Billy Coz, "The benefit being it can now create cool party synergy by giving the potential damage to a character who can gain advantage (Reckless Attacking Barbarian or Shield Master fighter for example), has a higher chance to hit (Archery fighter under the influence of a Bless spell or with Precision Attack maneuver), or even gets special benefits from a kill (GWM bonus attack, Fiend pact Warlock getting temp hp). All of those are why I suggested a d6 for damage. Even then, if this becomes a complete "go-to" cantrip I'd probably remove the +casting modifier rider." The bonus to hit in parenthesis is a small inducement to use the cantrip in other situations, but might not be warranted.

The duration extending solution was implemented in Baldur's Gate 3, which uses D&D 5th edition as a ruleset. The change feels balanced and was designed working with the 5th edition designers, so it feels legitimate.

Wall of Water

The volume of water is 60' wide, 20' high and 1' thick, or a dome that is 30' in diameter, 20' high at the middle, and 1' thick.

Otherwise probably won't protect against Fireball, which can go around corners.

Witch Bolt

At higher levels, increase the initial and ongoing damage by some small amount, such as half your proficiency bonus. 

Whenever the target takes damage from this spell, the target's speed is decreased to zero until the end of its next turn unless it makes a Constitution save.

Otherwise considered a minor problem by MelloRed because the spell is slightly weak.

Equipment

Additional Equipment

In addition to the official WotC equipment offered in the Sword Coast Adventurer's Guide and the Player's Handbook, there is more in the Adventures in Middle Earth Player's Guide, in addition to the veritable avalanche of items (magical and mundane) that can be pilfered from all the D&D 3.x books with little to no modification. Here is a thread of relatively useful items from those editions. 

And here's a good article on how to deal with masterwork items in 5e. TL;DR: just make them +1 items (this opinion seems to be shared across many threads on the internet). 

The designers and the studio that produced AiMEPG is very respectable and trustworthy. The 3.x books should be reviewed with a pinch of caution, but only become problematic when they allow for item interactions that allow switching items without an action or combinations that are equivalent to taking an ability score well beyond 20. For converting DCs, here's a handy chart:

3.x DC

5e DC

3.x DC

5e DC

3.x DC

5e DC

10

10

27

16

44

23

11

10

28

17

45

24

12

10

29

17

46

24

13

11

30

18

47

24

14

11

31

18

48

25

15

12

32

18

49

25

16

12

33

19

50

26

17

12

34

19

51

26

18

13

35

20

52

26

19

13

36

20

53

27

20

14

37

20

54

27

21

14

38

21

55

28

22

14

39

21

56

28

23

15

40

22

57

28

24

15

41

22

58

29

25

16

42

22

59

29

26

16

43

23

60

30

Additional Weapons

This weapon list is used, in addition to those found in the PHB. Or, this additional list.

Just some extra options for those who feel limited by the official weapons.

Adventuring Gear

This item costs 30 gp, weighs 20 lb., and has 5 charges. Spending a charge allows the PC to pull out any mundane item that they need. Examples of mundane items include: shovel; crowbar; grappling hook; torch, caltrops; oil flask; steel mirror. 

This functions similarly to Dungeon World's item of the same name. Without this house rule, veteran players who have previously thought of potentially useful tools feel obliged to add all of them to any character who can carry them. With this houserule, players who think of a tool during gameplay are rewarded for creativity, and players aren't forced to try to think beforehand of every tool that might possibly be useful during an adventure. From Sam Fletcher's house rules.

As an inferior alternative, there's a more complete list of mundane items here

Disability Remedies

Disabled characters have access to appropriate remedies.

This becomes necessary if the rules for injuries is used, hence the two colors.

Expected Magic Items per Level

Each character should gain approximately one consumable per level, and one permanent item that is actually helpful for that specific character every 4 levels. The latter includes one crazy powerful item found on Magic Item table I by 20th level.

This is a simplification of a detailed examination of the rules on what items the characters should find based on the rules in the DMG pages 83, 133, and the magic item tables. These are in addition to the expected wealth per level found elsewhere in the DMG, since the mantra of 5e has been that magic items are not commercially available. The only way in which the above simplification deviates from the actual math is that characters should gain some extra items by level 4 and then find fewer items by level 10 to make up for that. However, overall, the above simplification is accurate. 

There might be some additional or new rules about this in Xanathar's Guide to Everything.

Greataxe

Add 1d10 damage on a critical hit. 

When you roll a critical with a greataxe, you may make another attack with the weapon with disadvantage.

Otherwise weak when compared to a two handed sword and considered a moderate problem by MelloRed. The only corner case in which the Greataxe, which does 1d12 damage, is better than a two handed sword, which does 2d6 damage, is when a Barbarian's Brutal Critical is triggered, which allows the Barbarian to roll one additional weapon damage die. This still doesn't make it worthwhile.

A discussion on whether to make the additional die a d8 or d12 yielded this comment: 

The formula for the additional expected damage of +1d8 crit greataxes, compared to greatswords, is:

50% * -0.5 + 5% * (-0.5 * 2 + 4.5)

(replace 50% and 5% with 70% and 9.75% if advantage.  I'm assuming a normal hit chance of 55%)

without advantage this is -0.075, and with advantage this is -0.00875.

with 5.5 (1d10) it becomes -0.025 & +0.09, and with 6.5 (1d12) it becomes +0.025 and +0.18625.

so, even with advantage on every attack, it'll only be superior with +1d10.  and then it's very slightly worse than greatswords on normal attacks but very slightly better on advantage attacks.  so, I think 1d10 is the right number here

Healing Potions

Allow using Hit Dice and heal Hit Dice + (one less than stated dice) + Constitution bonus. E.g. a regular Healing Potion drunk by a first level fighter with 14 Constitution would spend a Hit Die and heal d10 + d4 + 2.

This makes healing potions scale with characters a bit and drain character healing potential at the same time. Taken from here.

Instrument of the Bards

This item grants disadvantage to all the saves made to spells cast by the bard wielding it.

Otherwise, the benefit of imposing disadvantage to saves only applies to spells using components to Charm a target, which are only Animal Friendship and Hypnotic Pattern, which seems a waste of a feature.

Magic Item Crafting

The downtime rules for crafting found in Xanathar's Guide to Everything (summarized here) are used.

A character able to contribute towards the crafting of a magic item contributes 5 gp per level per day in labor towards its production. If the item in question involves a spell the character can cast, the contribution is raised by 100 gp per level per day. If the character has proficiency in Artisan's Tools (Alchemical Supplies), the contribution towards the production of potions and other consumables is raised by 100 gp per level per day. All other rules in the DMG that don't conflict with these still apply: the DM, for example, can still require a specific component, spell, or other prerequisite be required to make an item.

Otherwise, under the DMG rules, it takes a 20th level character almost 55 years of continuous work to scribe a single 9th level scroll. Worse, with a permanent magic item, you have to consume the components of the spells that are required every day of the crafting process. 

With this change, that scroll only takes the better part of a year. And a Legendary magic item (requiring a 17th level crafter) still takes over 15 years to make. It might be worth cutting the cost in gp of making scrolls further as well, since it costs as much to scribe a scroll as it does to create an item of similar level.

If the Dungeon Master's Magic Item Guide is used, that also contains alternative crafting rules, which may be adopted instead. The same can be said for Dante's House Rules, which contains several interesting ways to create a variety of non-mundane items, or for AeronDrake's Equimpent rules, both of which are good. One could even use the rules in the Wilderness & City GuideEven Mike Mearls has said that there will be an upcoming Unearthed Arcana variant rule on crafting coming out at some point, but perhaps he was referring to the UA downtime activities, which don't really fix this issue. However, those rules were updated in Xanathar's Guide to Everything.

This might also work, but I have not thoroughly checked it.

Magic Item Properties: Temperate 

Suffers no harm from temperatures. 

Otherwise, the wording of this minor magic effect in the DMG makes the owner immune to all damage from everything if the environment were in the right (normal) temperature range. This could be considered a clarification. Otherwise considered broken by MelloRed.

Magic Item Prices 

The values in this supplement are used. 

Otherwise, the range of values given on page 135 of the DMG is pretty big, and sometimes unreasonable. While the advice given that magic items should not be available for trade is nice advice, it's really not realistic in a campaign in which more than a token number of magic items exist

The supplement is discussed and criticized here. It should be noted that it breaks with the rules in the DMG and is not consistent in pricing things by rarity. For example a legendary Ring of Invisibility is priced at 10,000, while a merely rare Ring of Free Action is 20,000 gp. However, the prices seem to be consistent with actual utility: the aforementioned rings have similar utility, although the latter is arguably slightly more useful, and since the prices increase geometrically, that premium could conceivably double its price. 

Minimum Damage

The minimum damage an attack can do is zero. 

From this sage advice. I don't really like this, since it basically turns a hit into a miss, but it's easy to house rule a minimum damage of 1 if you don't like the official rule.

Poison DCs

The DCs provided for the poisons in the DMG are each increased by 1. 

This makes them slightly more reliable to use, given how large of a gold-sink they are. Taken from Sam Fletcher's house rules.

Potion Consumption

Drinking a potion yourself only takes a Bonus Action. Feeding one to someone else is an Action. 

Otherwise this kind of item rarely sees use in combat, especially at high levels, where actions become very valuable, and getting hit by an attack will probably undo the benefit of a potion, so it almost always makes more sent to attack than to heal yourself, even if the enemy might drop you below zero (and even if the extra penalties for dropping to 0 hp suggested in this document are adopted). Without the house rule, it takes your free object interaction to get the potion in your hand and then your regular action to drink it. The cost of a potion (along with the fact that it's a common magic item) is enough of a resource that players will still use them sparingly. This house rule becomes more compelling if there are house rules punishing going to 0 hp or failing death saves. Taken from Sam Fletcher's house rules.

It's debatable whether drinking a potion should cause an attack of opportunity. Worth thinking about.

Rituals

Spells with the Ritual tag can be cast by some without consuming a spell slot if you take 10 minutes longer to cast the spell. 

Bards can cast any ritual spell they know as a ritual. Clerics and Druids must have the ritual spell prepared to cast it as a ritual. Wizards can cast any ritual spell in their spellbook as a ritual, prepared or not, as long as they have their spellbook. Pact of the Tome Warlocks can cast any ritual spell from any class thanks to the Book of Ancient Secrets feature. Path of the Totem Warrior Barbarians can cast three spells as rituals. And characters with the Ritual Caster feat can cast ritual spells of the selected class as long as they are in the character's ritual book, if the spell is no higher than half the character's level, and the character is holding the ritual book.

Merely a clarification of the different ways rituals work. There are more limitations than these, but the other limitations are universal.

Shield Doffing

Doffing a shield can be done using the free use of an object interaction, similar to drawing or dropping a weapon. 

Donning a shield still requires an Action, but this provides a little bit more flexibility in combat, allowing for dramatic actions. Taken from Sam Fletcher's house rules.

Silver Standard

The most common coin in circulation is a silver coin, not a gold coin. All prices are usually expressed in silver or copper, not gold. 

This is merely for the sake of realism, and to add social value to gold. Here is some info on the various metals used as currency.

Spears Are Polearms

For the sake of the Polearm Master feat, and for any other purpose, spears are polearms.

This seems like an oversight, since quarterstaffs are polearms, and mounting a pointy metal tip on one end shouldn't undo that. 

Spell Components, Focus, & Item Interaction

For spells that have material components, if you have a Component Pouch or appropriate focus, and, for spells requiring vocal components, the ability to speak, you've met the requirements to cast any spell with any class: you no longer need a free hand or to use Item Interactions. Expensive or rare material components for a particular spell are still required to cast that spell. The other ways to cast a spell, where given, still remain available.

Otherwise, to cast a spell, you need a free hand to use a free object interaction to draw material components, and another free hand to use somatic components and, if you have one, wield a focus, which can replace inexpensive material components. This problem applies to anybody that might be holding two weapons or a weapon and a shield, which includes bards, clerics, paladins, rangers, eldritch knights and arcane tricksters. The game was designed to eliminate the pedantry that goes along with sorting out this kind of bullshit, as the game's lead designer has said. This solution slightly erodes the utility of the Warcaster feat, of which this houserule wholly reproduces one out of three benefits, but the feat remains worthwhile. Plenty of detail about this here.

Starting Gold

See Starting Gold in character classes, because related to character creation.

Strongholds

Either Matt Colville's Stronghold Rules or these rules are used, along with the Mercantile Supplement.

Matt Colville's rules are very thorough, but cost more than the alternative, and both are adequate. A reference to stronghold rules also appears under Downtime Activities, because Strongholds are mostly administered during downtime, but they're cross-posted here to highlight that there are additional options. The mercantile supplement is mainly a way to note what additional equipment the characters might have access to.

Swimming in Medium or Heavy Armor

Athletics checks to swim in medium or heavy armor are made with disadvantage.

Otherwise, I mean, come on.

Thrown Weapons

Thrown weapons that are light, as well as javelins and darts, gain the ammunition property

Otherwise only one can be drawn as a free object interaction per round, limiting the number of thrown attacks characters with multiple attacks can make. The weapons benefitting from this suggestion would intentionally exclude tridents and spears. Considered a moderate problem by MelloRed.

Tool Proficiencies Expanded

Being proficient in a tool grants advantage on rolls related thereto, and can open up extra options, as outlined in Xanathar's Guide to Everything. The rules presented here are used. These proficiencies can also generate income as clarified under Downtime Activities.

Under the rules there’s little mechanical reason to not pick poisoner’s kit or thieves’ tools as a tool proficiency. While everyone likes to roleplay, it would be nice if choices to role-play were not be punished with a mechanical sacrifice. The linked product is well-reviewed, and introduces rules for what to do with those other tool proficiencies in the PHB. It also limits their utility by making spell like slots. As an alternative, here's some other rules for Herbalism and Alchemy and there are more for alchemy in the Wilderness Survival Guide.

Herbalists could also brew potions of healing under the Downtime rules, Craft antitoxins, or simply work.

Vehicles and Ships

If necessary, these rules are used for ships and vehicles. 

Occasionally, the need to have more detailed rules for vehicles will arise. These rules are the best such expansion I've found, but it's still pretty short on examples and options.

Gameplay

Action Options 

Found in DMG Chapter 9, are interesting, and encourage the type of play I enjoy (climbing on larger creatures, shoving, tumbling, etc.), but a couple of them (marking and disarming) might change the game a bit. 

The flanking rules might be slightly dangerous because they erode the utility of other sources of advantage. This problem is resolved if advantage stacking is allowed.

It's also worth noting here that the marking rules can provoke many attacks per round, which may be unbalancing for classes that rely on a few high damage attacks, such as the rogue. Making such an attack use the character's reaction might resolve this issue.

Attack Spells targeting Magic Resistance

Attack spells have disadvantage on attack rolls against targets with Magic Resistance feature from the DMG. 

Otherwise, while Magic Resistance grants advantage on saves, it is of no assistance against spells that have attack rolls targeting AC. While this distinction might make sense when comparing an attack roll with a Wisdom save, it fails when comparing with a Strength save, wherein both spells are physical forces trying to affect a target's body. 

Buy-In from Players

When the DM announces an event, it's the players' responsibility to figure out a reason why their character would want to get involved in that event. As Jim McClure (of One Shot Podcast) said: "You can choose HOW your character is interested in the adventure, not IF your character is interested." This rule should obviously be invoked only when necessary.

Stolen from here (and from Feng Shui 2).

Casting More than One Spell per Round

If you cast a bonus-action spell, the other spells you cast that round must be cantrips

If you cast a reaction spell while casting an action spell, both spells are cumulatively and independently subject the somatic, verbal and material component restrictions. You can't use one hand for the components of both spells.

This first sentence clarifies what is already in the rules, on page 202 of the Player's Handbook, under the Casting Time: Bonus Action. Otherwise, Fireball + Eldrich Blast + Agonizing blast is a bit much in one round, particularly at high level. I'm not sure why I added invocation to the sentence: that might be arguable.

The second sentence clarifies that the first doesn't restrict anything more than casting bonus-action spells. Unless the reaction spell and the other spell have independently fulfillable component requirements (i.e. not more than one of the spells has verbal components, and, if both have material or somatic components, you have both hands free), you won't be able to cast the reaction spell in the middle of casting the other spell. It should be noted that the clarification offered at the end of this Sage Advice Compendium conforms with this clarification, since Counterspell only has a somatic component. But the spirit of the simple clarification advocates in favor of simplifying spell component interactions, as I and others suggest elsewhere in this document.

Casting Rituals while Moving

You may move while casting rituals.

Clarified in this bit of Sage Advice.

Climbing a Larger Creature

Every round, you may roll Athletics or Acrobatics if you don't have a climb speed, and such movement is difficult terrain, and even just staying on requires a test if you're not somehow "latched on." Reaching certain points (e.g. eyes) might grant vulnerability or even automatically score a critical hit. Creatures may Shake off as an action, requiring all climbers to repeat their test as a reaction.

Stolen from here.

Dis/Advantage: -/+5 on Passive Checks

Each gives +/-5 respectively to passive checks. These bonuses do not stack. 

Source: PHB page 175, under Passive Checks.

Downtime Activities 

The Xanathar's Guide to Everything options (summarized here) for this should be used, instead of those in the Player's Handbook and the Dungeon Master's Guide. Over periods longer than a few weeks, the average results for rolls should be taken, and the DM determines what complications may or may not arise, at her discretion.

These expand the rules in the DMG to provide extra detail if desired. Even though, it is still, in all ways, better to just be a wizard with fabricate than to actually try and craft something with the XGtE rules. Also, those XGtE rules offer no way to use the actual crafting "skill" no matter how good it is. It also addresses some, but not all, of the magic item creation issues, and has some problematic timelines (30 weeks of full time work, 15 if you have an apprentice, to create a suit of plate armor is rather long). However, I'm not sure there will ever be a one-formula-fits-all mechanic to figure out how long it takes to do a thing, so these might as well be it. Also, it includes a system of NPCs who actively oppose the characters, Buying Magic Items, Selling Magic Items, Crafting Magic Items, Scribing a Spell Scroll, Carousing, Crime, Gambling, Pit Fighting, Relaxation, Religious Services, Work, and Training, which is pretty impressive.

Running a Business

Use the rules for Running a Business

This is distinct from practicing a trade you are trained (proficient) in, which is the last section in the UA link above.

Building and Maintaining a Stronghold

Either use Matt Colville's Strongholds & Followers rules, or use the rules for building and maintaining a Stronghold of some kind (along with that supplement's Mercantile expansion). 

The link on strongholds includes some additional detail on skilled hirelings, which is very welcome. It also fixes the problem the DMG rules for strongholds wherein workers actively destroy the building while PCs are away. The mercantile expansion is merely a way to gain access to interesting equipment

Require Training to Gain a Level 

To make the characters' acquisition of new features more plausible, the additional training detailed in these rules is required. 

This addresses the somewhat meteoric rise to power that most characters see in many campaigns, where they go from common folks to superheroes over the course of a handful of months. It should be said that the document's author would make this yellow, but it doesn't seem to hamper the enjoyment of the game very much, so it's green.

Eliminate Bonus Actions

Merge bonus actions into actions. For example: "When you cast this spell, you can also take one of the following actions: attack, cast a cantrip, dodge, dash."

Mike Mearls doesn't like bonus actions. It seems like they are too finicky, require extra rules. I'm not sure I agree or disagree, but, hey, he's the name on the books, so it's worth mentioning.

Falling Damage

Immunity to non-magical bludgeoning damage doesn't protect from falling damage.

This is just a clarification from Sage Advice of June 2016

Fleeting Luck 

Each PC begins the game with 1 point of fleeting Luck. Fleeting Luck is awarded to a PC each time the character achieves a critical success (usually rolling a natural 20 on an action), performs cool (or foolish) actions, or when the judge deems the PC deserves recognition. There is no limit to the amount of fleeting Luck a PC may have at any time. Fleeting Luck can be spent to modify a PC’s die roll or to aid another PC on a 1:1 basis. Any PC can spend his fleeting Luck to aid another and multiple PCs can assist a single party member if desired. Fleeting Luck vanishes whenever a critical failure occurs, usually in the form of a natural “1” on an action. Fleeting Luck is not lost if the “1” result does not result in failure, such as when rolling to determine initiative score or a skill check. Whenever a PC rolls a critical failure, ALL the PCs lose their fleeting Luck.

From Goodman Games' Lankhmar, these are an excellent alternative to Inspiration that avoids players hoarding them. Another alternative is Hero Points.

Followers

Either use Matt Colville's Strongholds & Followers rules or these rules for followers. The latter are triggered at level 10 and later, or when a character builds a stronghold. The DM may elect to roll three times and choose the outcome, or to mix and match some of the followers from different results.

The DM should feel free to strike certain results, since they can be very powerful, especially if triggered by PCs building strongholds at low levels. Again, Matt Colville's Stronghold rules might be better – they're certainly more extensive.

Fronts

The DM should note the organized or related threats in the world, and then just have them advance towards their goals when the PCs don't stop them.

Stolen from the Apocalypse World system, and allows a more sensible plot tracking system than just improvising it. More details here. As an alternative, use the Stars Without Number Faction system.

Hero Points 

Found in DMG Chapter 9, are an excellent alternative to Inspiration. I would toy with both, and then make a determination. Another alternative is Fleeting Luck.

Healing Surges 

Found in DMG Chapter 9, and allows using HD to heal in combat. I liked this in 4e because it made a dedicated healer a smidge less indispensable. However, the number of surges might be a bit high, and it's worth considering lowering them by two.

Hireling Morale 

Hirelings have a Morale bonus, which starts as the hiring PC's Cha bonus. This can be modified up or down for the hireling's background, character traits, pay, and the kind and quantity of tasks the hireling has been given. Roll Morale as a skill to overcome a DC based on the danger when there is some threat to the hireling's well-being or livelihood. The outcome determines whether the hireling acts out of loyalty to the PC or to him- or herself. A slight danger, such as that imposed by foraging in a scary forest, might have a DC of 10, while a Dragon might have a DC of 20 or more.
This doesn't change the fact that hirelings don't usually go adventuring, even though they might accompany PCs while travelling in dangerous areas.

I wouldn't bother with figuring Morale out until it's necessary to roll it, and just note the events that might affect the score until then. More rules on Hirelings on page 159 of the PHB, on page 94 of the DMG, and under the Stronghold supplement linked under Downtime Activities, above. In no particular order, here are some possible untrained hirelings:

Nightwatchman*

Groundskeeper*

Assistant*

Maids

Crier

Cook*

Butler*

Footman

Lady's Maid

Porter

Valet*

Groom* 

Stable hand*

Linkboy

Handyman*

*Hirelings marked with an asterisk can easily range from Untrained to Skilled, and in the latter case manage teams of hirelings, and require higher pay. The Nightwatchman, in this case, is not a mere guard, but something closer to a Captain of the Guard.

Holding Breath in Combat

When holding your breath, the same rules used to concentrate on a spell are used to concentrate on holding your breath. 

For example, taking damage requires a Constitution Saving Throw. You may still concentrate on a spell that requires concentration while holding your breath. Similarly to the rule above, this helps make fighting underwater a bit more risky, like you would expect it to be. It helps distinguish between swimming around peacefully, and being in a violent conflict underwater; something the default rules don't do. Taken from Sam Fletcher's house rules.

Honor & Sanity, Fear & Horror 

Found in DMG Chapter 9, these might be interesting to mix into Lane’s Shadar-Kai dominated world.

Initiative

Some of these are from DMG Chapter 9:

Initiative Score 

Turns initiative into a score by adding 10 to the bonus. I actually prefer doing this just for monsters and NPCs, to lower the swing from 2d20 (when both a PC and a Monster rolls) to just 1d20. Billy suggests turning the d20 into a d10 for even less swing (in alternative or in addition to the prior idea), warning that this makes characters with a high initiative bonus.

Side Initiative 

Turns initiative into a simple 1d20 for each side, end of story. I think this is not that interesting. However, it is similar to what I would suggest:

NT's Initiative 

Each PC rolls their own initiative, but the bad guys roll a single initiative with their best modifier (or simply use their best Initiative Score as defined above). 

The PCs that roll better go first on the first round, followed by the bad guys. But then the all PCs and all the bad guys just alternate their turns as a group, acting in any order within their turn. This makes combat a little less crunchy in terms of figuring out initiative changes, readied actions, and such.

No Initiative

The DM decides who goes and in what order. Actors with high initiative are usually going to go first. 

This isn't as bad as it sounds. Combat will generally go faster, and it will be coherent. Plus, the DM can skip around if players are not sure what they want to do. Or simply go around the table in a circle. This will only work in groups that are comfortable sharing the spotlight.

When to roll initiative 

The action that starts combat goes off before initiative, and is not part of the initiative sequence. As it is being resolved, initiative is rolled. 

As Mike Mearls, the game's lead designer, pointed out, combat shouldn't start with the slowness of figuring out initiative. It should start with the thing that started combat. Then, as that is resolved, get initiative sorted out. This also insures that you don't get the weird result where someone suddenly does something that others react to with combat, but the dice roll say that the action that triggered those reactions happens later in the round. Which is weird.

Injuries 

If you fail your second death save before recovering all of them a death save by more than 5, roll twice on the injury table and pick one result. If two death saves are failed, pick an appropriate disability

Alternatively, use these Mishaps and Maladies.

Found in DMG Chapter 9, these make combat more scary, which makes the DM's job of bringing drama into combat easier, so it's worth looking at. I dislike the idea of triggering them off of critical hits or just dropping to 0 HP: these events happen too often. However, triggering them off of badly failed death saves (or simply a second failed death save) might instill a healthy fear of those situations, which otherwise aren't that scary. I would also allow a player to roll twice and pick the injury, just to give them a bit of flexibility, since, for example, disadvantage on ranged attacks can be crippling for a ranged character. 

While both rules need not be used, the second part of the rule, linking to disabilities, makes the game more inclusive, and even allows implementing the disability superpower trope. It allows a range of measures to overcome the disability, including guide animals, which is why I also link this resource in the equipment section.

The alternative seems like a more complete, better fleshed out system, but adds some complication that may not be welcome.

Two colors because either this or the Zero Hit Point rule would alleviate the issue that dropping a PC is in no way alarming.

Inspiration: Session Statement

If a PC starts a session without inspiration, the player can determine a previously undetermined fact about the PC. It can be about the PC's background, personality, or anything that the DM agrees with. 

This encourages character development and is an additional way to give out inspiration, which is a fun game element.

Inspiration: Additional Uses

You can spend an inspiration to gain one of the following benefits, however you cannot spend more than one inspiration per round. 

  • You can re-roll a d20 roll you just made.

  • You can gain a +5 bonus to a single d20 roll.

  • You can take an additional action or reaction (as if you had taken the readied action).

  • You can regain a number of expended spell slots that have a combined level equal to half your proficiency bonus (rounded up).

  • While unconscious, you can become stable.

  • You can gain a hint from the GM

  • You can use this to attempt an otherwise unusual or special maneuver or action. (Note: this just allows the attempt, not success).

Stolen from the Terra Rynn House Rules. The first option is widely used. The others are simply good suggestions. And there's really no reason other than simplicity of play to forbid characters from accumulating more than one Inspiration point.

Knocking a Creature Out

Unless the weapon used to deliver the knock-out blow is specifically made for such purpose, the target gets a Constitution save to avoid being knocked out (and the damage that goes along with it). 

For reference, PHB (page 198): "When an attacker reduces a creature to 0 hit points with a melee attack, the attacker can knock the creature out. The attacker can make this choice the instant the damage is dealt. The creature falls unconscious, and is stable." The issue here is that it's a pain in the DM's neck to allow all combatants to be interrogated by the PCs, and it's unrealistic to allow a two hander to knock everyone out. I don't feel strongly about this.

Level Drain

Attacks that drain a level impose a cumulative -1 to all ability rolls (including attacks, saves and skill checks). If the absolute value of this penalty is equal to or greater than the target's level, bad things? happen: the character becomes a vampire, a wight, a ghost, or whatever. Every long rest, the target gets a Constitution save to reduce the penalty by one. The DC is equal to the absolute value of the penalty plus 10.

Otherwise, when things like vampires achieve certain hits, you have to recalculate max hit points for the target, which is somewhat more complicated and annoying to administer. This suggestion is stolen from 3.5/pathfinder. A good alternative is just using exhaustion, but that might be extreme, since 6 levels of exhaustion cause death.

Level Gain Process

Feats, if used, are paid for using points per level as described in the su