David Perry firstname.lastname@example.org
Running The Game
Dungeon Rats is a hacking together of World of Dungeons and Maze Rats into a light, flexible, fiction-focused ruleset with the goal of smoothly running pre-written Old School adventures. In its current state, playing as GM assumes experience with Apocalypse Engine games such as Dungeon World, as well as Old School games such as Early D&D or its clones and derivatives.
Principia Apocrypha is a list of principles to evoke an Old School playstyle (based heavily on Maze Rats’ GM advice) that is well suited to follow for this ruleset.
If you are reading this straight through, note that most of the rules themselves are contained in the character sheet below, which will appear out of order.
To prepare for playing in person, print this page for reference while running the game, and the second page at least once for reference during character creation. Then for each player, print pages 3 and 4 on both sides of a single sheet, folding them like a brochure.
Create your own additional equipment and spell lists, or simply refer to those of other games (MR and WoD for equipment, B/X or TBH for traditional spells, or MR or Freebooters on the Frontier for Mercurial Magic).
Running pre-written old school adventures may require some conversion of different aspects. They should be easy enough to make on the fly while running the adventure.
Depending on the adventure, the Standard Piece (sp) coin could be gold or silver. For a long campaign, you may want to tweak treasure amounts found (such as treasure table results) to match a desired leveling cadence.
Compel a roll with a suitable Ability. A Failure could be as dire as the original. For a more challenging alternative, roll with only 1d6, +Ability+half of Level.
Use HD normally. AC may be translated into Armor for 1 Armor per 2 points of AC above 10 (Ascending – watch out for Descending AC, in which case subtract it from 20 first). Damage can be dealt normally on Failures and Partial Successes (high-damage attacks only on Failure) of interacting with the monster. Special abilities of the monster may also be provoked on Failures or Partial Successes, or when it makes sense.
Player Character AC
For any change or difference in AC, first determine if it is more relevant to mobility, or to physical protection. For mobility, modify the character’s DEX Score. For physical protection, apply it to Armor, by dividing the value by 2, rounding down, with a minimum of 1. So a noted reduction by 1 would have an effect of -1, but a reduction by 4 would have an effect of -2.
A normal roll can be used to determine the reaction of an NPC or monster the party encounters, using an ability suitable to the specifics; such as CHA for townsfolk, or STR if one of the PCs is attempting to intimidate a foe.
Usually monsters from adventures will have a Morale value. To test whether they flee in a suitable situation (when a fight is clearly going against them, or when their first companion dies), roll 2d6 ; if the result is above their Morale, they flee.
For monsters with no Morale value, either set a plausible value to beat, or use a normal roll similar to reaction rolls.
Consequences & Complications
In general, if you are running a pre-written adventure, you likely wish to avoid narrating consequences of Failures and Partial Successes that distort the written truth of that adventure. It’s ok to not push PCs forward constantly with disruptive Apocalypse Engine style consequences.
If something should happen but you don’t know what, you could roll the Dungeon Die. If it’s only a Complication of Partial Success, you might wish to re-roll Encounters.
Example Consequences & Complications
Point out a downside or side effect of their action
Deal 1 Damage from exhaustion or exposure
Threaten items in their Hands or Belts
Take up time; roll the Dungeon Die
Reap a resource; roll the Supply Die (if used)
Take their Pack, or something extra they’re carrying
Mess with a Wizard’s spells
Have hirelings make trouble
Reveal that a Danger has already impacted them
The Dungeon Die
When a roll is failed and it’s not obvious what will happen in the current situation, or when an action requires time to pass in-game (roughly 10 minutes), roll the Dungeon Die:
1. Abilities: Roll 3d6 for each Ability. The GM may allow you to instead roll 4d6 and drop the lowest, and/or swap the values for two Abilities. Note in your sheet the total Score and matching Modifier:
2. HD & HP: You start at a fresh 6 HP, and have Hit Dice equal to 1 plus your CON Mod if it is positive.
3. Background: Roll a background. Backgrounds let you attempt things you otherwise would not.
4. Class: Choose a class, and roll or choose three of its Skills.
5. Persona: Roll or choose as desired for your name, appearance, personality, etc.
6. Gear: Everyone gets a Tinderbox, a Small Weapon, 4 Random Items from the Maze Rats list.
Clerics get Light Armor and a Martial Weapon, a Book of Scripture, Holy Symbol, 2 Vials of Holy Water.
Fighters get a Martial Weapon, a Helmet, and either Light Armor and a Great Weapon, or a Shield and Medium Armor.
Thieves get a Light Armor and a Martial Weapon, and can pick three more items from the Maze Rats list.
Wizards get Light Armor, a Book Half-Full of Arcane Notes, an Inkpot and Quills, and a Pouch of Dubious Content.
7. Relationships: After everyone is finished, decide how you know each other, and why each of you are broke and driven to tomb-robbing.
Small (10sp): 1D6 – May be thrown (1D6-1)
Martial (30sp): 1D6+1
Great (40sp): 1D6+2 – Requires both hands to use, only one may be carried, by hand. May be ranged (1D6+1).
Shield (10sp): +1 Armor. Can choose to destroy instead of taking damage. Only one may be carried, by hand.
Light (30sp): 1 Armor
Medium (150sp): 2 Armor
Heavy (1000sp): 3 Armor
See lists from Maze Rats or World of Dungeons.
Supply represents the entire party’s mundane supplies including rations, fuel for light, ammunition, medicants, and the condition of equipment like tents, bedrolls, and treasure sacks.
Similar to an Ability Score, ranging from 0-18, and translates to a Modifier just like an Ability. It starts at 15 for a group of 1-2, 17 for 3-5, and 18 for 6 or more, including hirelings and pack animals. Track it below.
When you need a meal, light, ammo, simple healing, make a roll plus Supply. Complications and Consequences are determined by the GM, but might include decreasing the Supply score by some amount, extra time taken while cooking or repairing something, a restless night from spoiled rations or degradation of shelter, or completely running out of one of the types of resources.
The GM chooses which Magic Variant to use:
Vancian Spellcasting Variant
The Wizard has a spellbook with three first-level spells from a list provided by the GM; choose one, randomly select two others, and note them. New spells must be found while adventuring.
Each long rest, the Wizard studies their spellbook and re-memorizes spells of a total amount of Spell Levels equal to twice the Wizard’s Level. Mark currently memorized spells with a star.
Casting a spell requires a free hand and a roll. The spell might be forgotten as a complication or failure.
Mercurial Magic Variant
Mercurial spells coalesce in a Wizard’s mind from ambient arcane energy mixing with thought. Conceiving a new spell requires time, a mind open to the ethereal realm, and an INT roll, which may be further modified by time spent (positively), how many spells you already hold in your mind (negatively), and other factors.
When you succeed in conceiving a spell, the GM will either tell you what it is, or ask you to roll for a random spell on a table. Intentionally hunting down specific spells out of the ether is possible, but is a long, risky process.
Casting a spell requires a free hand but is usually simple and quick, not requiring an Attempt. For spells composed of only a name, say what kind of effect you’re trying to create given the nature of the spell, and the GM will determine how it specifically manifests. The spell is gone from your mind after it is cast.
Sleep may allow spells to escape, and sudden unconsciousness may cause spells to be accidentally cast with catastrophic effect. If you have the Scribe skill, you can attempt to write a spell into a formula, which removes it from your mind, but makes it easier to conceive again, which may be done many times.
Usually, actions are resolved by the player explaining what their character does and how, and the GM will describe what happens.
Having an applicable background or just sufficiently preparing or finding situational advantages may save you from any failure. But…
When you attempt something difficult, risky, or uncertain, explain what you try and how you try it. Then roll 2d6, and add what the GM tells you (usually an Ability Mod). A total of…
10 or more is a Full Success; you do it.
7-9 is a Partial Success; you do it, but there’s a Complication: the GM will offer a hard choice or impose a cost in resources, time, energy, or a troublesome side-effect.
6 or less is a Failure; you don’t do it, and there’s a Consequence, potentially severe.
The GM may reveal potential Complications and Consequences before rolling; ask if you’re not sure.
If you have Proficiency from a skill that is applicable to the attempt…
6 or less is a Narrow Success; you do it, barely, but there is still a Complication or Consequence.
Combat takes the form one or more Attempts. On Successes, you may deal damage (see weapon list), -1 for improvised weapons and -2 if unarmed. Damage may be dealt to you as a Complication or Consequence. Normal physical damage is absorbed by Armor 1-for-1.
HP doesn’t only represent physical damage, but includes stamina and capacity to fight. In addition to combat, simple exhaustion, exposure, or other threats may reduce hit points directly.
After a meal and a long rest, you may heal: roll all of your Hit Dice, and keep a number of them equal to your level, adding them together. If the result is higher than your current HP, take the new value. If you are attended by a healer, roll an extra hit die.
Attempts to heal another without resting may be made, for 2 HP on a Full Success and 1 HP on a Partial Success. Complications and Consequences may include no more healing this way until resting.
When damage brings you to 0 HP or less, it could be lethal. The GM may allow a roll to determine if you get by with only a Severe Wound, in which case any damage beyond 0 HP goes directly to one of your Ability Scores (affecting the Modifier), and may have other descriptive effects, until expertly or magically treated. Otherwise, you die.
Background, Persona, Notes
Bless: Make holy water, or use holy water to anoint with divine protection
Cure: Attempt to heal wounds, remove curses, neutralize poisons by incantation
Turn: Attempt to hold undead at bay
Vision: Drink holy water to commune with your deity for its guidance
Adrenaline: Once since a long rest, when reduced below 6 HP, gain 1d6 HP
Hardy: Keep one extra HD when healing
Slay: Roll melee damage twice and choose
Tough: +1 Armor
Expert: Gain a Proficiency from any class
Reflexes: React quickly even if surprised
Sneak Attack: When attacking while hidden, roll damage twice and choose
Tinker: Attempt to quickly pick a lock, pick a pocket, or disarm a trap
Cantrips: Can always attempt 3 simple magics: Candle, Long Breath, Throw Voice
Sense: Attempt to sense magical energy, identify a magic item, read magical script
Spellcasting: (See Magic section)
Scribe: Attempt to write a known spell into a formula for later use
Gear – if there’s no room to write it, it might not fit
Hands – needed for light, spells, shield, great weapon
Worn – armor, clothes, adornments, dirt, blood, ichor
Belt – a few items or pouches you can retrieve quickly
Pack – ask the GM if it fits, slow to access, drop for mobility
You gain 1 XP for each Standard Piece Coin’s worth of treasure that you bring back to civilization, split among the party. When you level up, mark two different Advances: