Rules & Mechanics Cheat Sheet

Roll two 10-sided dice (one tens die, one units die). Attempt to roll equal to or under your skill or characteristic rating.

• 01 — Critical Success: Always succeeds; best possible outcome, bonus insights or effects.
• ≤ ⅕ Skill — Extreme Success: Outstanding outcome, weapon impale, maximum effect.
• ≤ ½ Skill — Hard Success: Required for difficult conditions, skilled opposition, or harsh odds.
• ≤ Skill — Regular Success: Standard successful execution.
• > Skill — Failure: Goal is not achieved.
• 96–100 / 100 — Fumble: Catastrophic mishap. (96–100 if skill < 50%; 100 if skill ≥ 50%).

Used to model superior advantage or severe handicap without altering the base skill percentage.

Note: If units die is 0 and the chosen tens die is 00, the result is 100.

When two active characters compete (e.g. Stealth vs. Listen, Arm Wrestling, Grappling):

Handling multi-step investigative challenges or whole-party attempts:

• Combined Roll: When an action requires two proficiencies (e.g. Spot Hidden + Track or Locksmith + Stealth). Both rolls must succeed unless the Keeper states only one is required.
• Group Checks: When the whole group tries to sneak past a guard, the player with the lowest skill rolls for the group, or the party rolls opposed against the guard's Listen/Spot Hidden.

• Hit Points (HP): (CON + SIZ) ÷ 10 (round down)
• Magic Points (MP): POW ÷ 5 (recovers 1 MP per hour)
• Sanity (SAN): Starts equal to POW; Max Sanity = 99 – Cthulhu Mythos
• Movement Rate (MOV):
  • If DEX < SIZ and STR < SIZ: MOV 7
  • If STR ≥ SIZ or DEX ≥ SIZ (or both equal): MOV 8
  • If STR > SIZ and DEX > SIZ: MOV 9
  • Age 40+: reduce MOV by 1 per decade after 40s.

Calculate STR + SIZ total:

Investigators may spend Luck points on a 1-for-1 basis to reduce a percentile roll to achieve success or upgrade to Hard/Extreme.

At the conclusion of a successful scenario chapter or significant adventure milestone, the Keeper may grant a Luck Improvement Check:

When an investigator fails a standard skill roll, they may request to Push the roll by taking a greater risk or taking extra time.

• Player Justification: The player must explain what they are doing differently to justify the second try.
• Exclusions: Combat rolls, Sanity checks, and Luck rolls cannot be pushed.
• Failure Consequence: If a pushed roll fails, the Keeper inflicts a dire consequence (e.g. alarm triggered, relic destroyed, injury, structural collapse, immediate Sanity loss).

All actions take place in descending order of Dexterity (DEX).

• Ready Firearms: A character with a firearm already drawn and ready to fire acts at DEX + 50 for their first shot!
• DEX Ties: Resolved by higher combat skill, or simultaneous resolution.
• Surprise: Ambushed targets cannot dodge or fight back on the first round (attacker gets +1 Bonus Die).

When targeted by a melee attack, the defender must choose ONE reaction:

Once a defender has dodged or fought back against an attack in a combat round, they become vulnerable to swarming:

Used to disarm, push, grapple, trip, or pin an opponent instead of inflicting direct HP damage:

• 1. Compare Build: If target's Build > your Build, take 1 Penalty Die per point of difference. If target is 3+ Build larger, maneuvers are impossible.
• 2. Opposed Roll: Roll Fighting (Brawl) vs. defender's Brawl or Dodge.
• 3. Pin / Hold: Once an enemy is pinned, all subsequent attacks against them gain +1 Bonus Die.

Achieving an Extreme Success (≤ ⅕ Skill) on an attack deals devastating damage:

• Impaling Weapons (Knives, Bullets, Spears): Maximum possible weapon damage + Max DB + Roll normal weapon damage again!
• Blunt Weapons (Clubs, Fists, Hammers): Maximum possible weapon damage + Maximum Damage Bonus.

Armor reduces incoming physical damage by a flat value before subtracting from Hit Points:

• Heavy Winter Coat: 1 point armor
• Leather Jacket / Helmet: 1–2 points armor
• 1920s Steel Vest: 6 points armor (torso only)
• Eldritch Monster Hides: 1 to 10+ points armor (magic/fire often ignores armor)

• No Fighting Back: Targets cannot Fight Back against ranged gunshot attacks from a distance.
• Point-Blank Range: Within DEX ÷ 5 in feet (approx. arm's reach), the shooter gains +1 Bonus Die!
• Range Increments:
  • Up to Base Range: Regular difficulty.
  • Up to 2× Base Range: Hard difficulty.
  • Up to 4× Base Range: Extreme difficulty.

When shot at, a defender who has not acted yet and is near cover may Dive for Cover:

• Defender rolls Dodge before the shot is resolved.
• If successful: Shooter suffers -1 Penalty Die on all shots this round.
• Consequence: Defender drops prone and forfeits their next attack action.

Handguns have a Rate of Fire (RoF) of 1, 2, or 3 shots per round:

• 1 Single Shot: Fired normally at standard difficulty with no penalty die.
• 2 or 3 Shots in 1 Round: Every single shot in that volley suffers -1 Penalty Die!
• Reloading: 1–2 rounds depending on clip vs. manual cylinder loading.

If an attack roll equals or exceeds the firearm's Malfunction Rating (typically 98–100 or 100):

• The weapon misfires, jams, or stovepipes without firing.
• Clearing a jam requires 1 full round and a successful Firearms or Mechanical Repair check.

12-Gauge Shotgun damage changes drastically with distance:

• 0 – 10 yards: 4d6 damage (Point blank = +1 Bonus Die)
• 10 – 20 yards: 2d6 damage
• 20 – 50 yards: 1d6 damage

Inflicted whenever a single attack deals damage equal to or greater than half maximum Hit Points (Max HP ÷ 2):

• CON Check Required: The investigator must immediately make a CON check or fall unconscious.
• Major Wound Marker: The investigator receives a Major Wound condition on their sheet.

An investigator dies instantly with no saving roll if:

• They suffer damage equal to or greater than their full Maximum HP in a single catastrophic blow.
• They are already at 0 HP and receive damage equal to or greater than their Maximum HP.

• Minor Wounds: Recover 1 HP per day of rest.
• Major Wounds: At the end of each week, make a CON check:
  • Success: Heals 1d3 HP (Major Wound removed).
  • Extreme: Heals 2d3 HP.
  • Fumble: Lose 1d3 HP or develop severe infection.

• Falling: 1d6 damage per 10 feet fallen (e.g., 30ft = 3d6).
• Fire / Burns: Minor fire (1d6/rnd); Fully engulfed (2d6/rnd).
• Suffocation / Drowning: Make CON check each round. On fail, suffer 1d6 damage per round until rescued.
• Poisons: Opposed POT vs. CON check.

• Initial Skim (Hours to Days): Gives an overview, inflicts initial Sanity loss, and yields a small initial Mythos boost (e.g. +1% Mythos).
• Full Study (Weeks to Months): Requires dedication and Language check. Awards full Cthulhu Mythos points, inflicts full SAN loss, and teaches included spells.

• Casting Costs: Spells always cost Magic Points (MP) and Sanity (SAN), and sometimes permanent characteristic points.
• First Time Cast: Requires a Hard POW roll (or ritual time/ingredients). Subsequent casts usually succeed automatically if cost is paid.
• Pushing Spell Rolls: Catastrophic spell backlash, summons wrong entity, or drains double SAN!

• MP Regeneration: 1 Magic Point recovers naturally per hour of rest.
• Dropping to 0 MP: The investigator falls unconscious from magical exhaustion.
• Burning Hit Points for MP: Once MP is 0, a caster may sacrifice 1 HP per additional Magic Point required!

Compare the Movement Rate (MOV) of all participants:

• Base Speed: Character with lowest MOV has Speed Rating 0.
• Action Points (AP): Each participant receives 1 AP + difference in MOV. (e.g. MOV 9 vs MOV 7 gets 3 AP per round).

• Spending AP: Spend 1 AP to move 1 Location forward along the chase track.
• Obstacles / Hazards: Passing a barrier (e.g. fence, crowd, wet floor) requires a skill check (Jump, Climb, Drive Auto).
• Failed Obstacle: Forfeits 1 AP or suffers damage/fall.

• Melee Attack: If in the same location as target, spend 1 AP to initiate attack.
• Ranged Attack: Can shoot at target in adjacent locations (subject to range penalties and moving vehicle modifiers).