Achtung! Cthulhu

The Secret War

It is World War II. The whole world is burning. But behind the headlines, a Secret War rages — between Allied occult intelligence services and Axis cultists, sorcerers, and mad scientists who have learned the truth of what lurks at the edges of reality.

You are an agent: a soldier, scholar, spy, mechanic, or occultist recruited because you saw something you weren't supposed to see, survived something nobody else did, or asked the right question in the wrong library. You fight for Section M (British) or Majestic (American), alongside French resistance and the brave peoples of every occupied nation.

The enemy is not just Nazis. It's the Black Sun, a sorcerous arm of the SS. It's Nachtwölfe, their weird-science rivals. It's the Deep Ones in the Atlantic. It's the alien Mi-Go in the mountains. It's Nyarlathotep, the Crawling Chaos, and behind him, dread Cthulhu himself.

This is pulp horror. The odds are stacked, but your agent is brave, clever, and lucky. Heroes make a difference here. Embrace the cliches. Deliver the one-liner. Make the once-in-a-million shot. Then punch evil right in the tentacles.

Factions

How The Game Works

The 2d20 System is designed to feel like a pulp movie. You and your fellow players collaborate on a story. The GM presents situations, plays all NPCs, and decides when the dice come out. You roll dice whenever success is uncertain and interesting.

There are only a few concepts to remember to play:

• Attributes (1–14): raw potential — Agility, Brawn, Coordination, Insight, Reason, Will.
• Skills (0–5): trained ability — Academia, Athletics, Fighting, etc.
• Focuses: specialisations inside a skill (e.g. Handguns, Occultism, Urban Survival).
• Truths: short phrases describing who you are or the scene around you.
• Talents: special rules-bending abilities your agent has earned.
• Three currencies: Momentum (yours), Threat (the GM's), Fortune (personal luck).

The Dice

You will use two kinds of dice:

d20 — Skill Dice

Twenty-sided dice. You roll 2d20 to resolve most tests. You can buy up to 3 more d20s (max pool 5d20).

Challenge Dice (CD) — Damage & Effect

Challenge Dice are specially-marked six-sided dice. If you only have normal d6s, read them like this:

An Effect triggers every special ability listed on a weapon or spell.

Making a Test

1. The GM tells you which Attribute + Skill to use. Add them together — that's your Target Number (TN).
2. The GM sets a Difficulty (0–5). Most are 1.
3. Roll 2d20 (or more if you've bought extra).
4. Count successes:
   • Each die ≤ TN = 1 success.
   • If you have a relevant focus: each die ≤ your skill value = 2 successes.
   • Each natural 1 = 2 successes.
   • Each natural 20 = a Complication.
5. If successes ≥ Difficulty → you pass. Any leftover successes become Momentum.

Buying Extra Dice

Before you roll, you can buy up to 3 extra d20s. Each one costs Momentum:

• First extra d20: 1 Momentum
• Second: 2 Momentum
• Third: 3 Momentum

You can also pay Threat to the GM to buy dice instead. The GM loves this — it gives them ammo later — but sometimes it's the right call.

Assisting

Another agent can roll 1d20 at their own TN to help. Their successes stack with yours if you score at least one. Describe how you're helping — a hand up a cliff, a word of encouragement, a cover fire burst.

Momentum — Your Resource

Momentum is a group pool shared by all players. Max 6 at any time.

You earn Momentum from excess successes on passed tests (one per extra success). You can spend it on any test, on anyone's turn.

Common Spends

Threat — The GM's Resource

Opposite to Momentum, the GM has Threat. They start each session with 2 Threat per player and gain more when:

• You choose to pay Threat instead of Momentum (to buy dice, or to buy off a complication).
• The scene becomes dangerous or an alarm is raised.
• An NPC generates unspent Momentum — it converts 1:1 to Threat.

The GM spends Threat to empower NPCs, summon reinforcements, change truths, or make scenes worse. It's a natural tension mechanic — sometimes the right move is to feed the GM in exchange for a critical advantage now.

Fortune — Pulp Luck

Each agent starts each mission with 3 Fortune (max 5). You may spend 1 per non-combat scene and 1 per round in combat.

Use Fortune for moments that matter. Don't hoard all of them.

Truths

A Truth is a short phrase that describes something about your agent, an NPC, or the scene. Your agent starts with at least four — drawn from Archetype, Background, Language, and Nationality.

Mechanically, a Truth can:

• Lower a test's Difficulty by 1 when it clearly helps.
• Raise it by 1 when it clearly hinders.
• Make something possible or impossible.

You can create new truths during play — by spending 2 Momentum, by spending Fortune (Make It Happen), or when the narrative clearly supports it. Truths can also change or be removed over time.

Combat in a Nutshell

Combat is tense but fast. The GM picks who starts. Turns alternate PC ↔ NPC until all have acted, then the round resets.

Zones & Range

On Your Turn

• 1 Major action (the big thing — Attack, Cast a Spell, Rush, Create Truth, etc.).
• 1 Minor action (Aim, Draw Item, Move, Prepare).
• You can spend 1 Momentum for an extra Minor, or 1 Fortune (once/scene) for an extra Major.

Attacking

1. Declare target + weapon.
2. Roll the skill test:
   • Melee — Agility + Fighting, opposed by target's same roll.
   • Ranged — Coordination + Fighting.
   • Mental — Will + Academia, opposed by target's Will + Resilience.
3. If you hit, roll the weapon's Challenge Dice for stress.
4. Subtract target's Armour + Cover (or Courage + Morale for mental).
5. Apply remaining stress; check for injuries.

Cover

Use it. A sturdy object gives Cover 2 (stacked with Armour). Rolling behind something is usually a minor action.

Ammo

You don't count bullets. You have 3 Ammo as a currency used for Salvo shots that add special effects (Area, Stun, Vicious…). Regular shots never run out.

Stress, Injuries & Healing

Your agent has a stress track. Take damage, fill it up.

Injuries Trigger When

• You take 5+ stress from a single source (after Armour/Cover).
• Your stress track fills up.
• You take more stress while already full.

Each injury raises your Complication Range by 1. 3 injuries (in any combination of physical/mental) → you are Defeated and out of the scene. If your injuries are mostly physical, you're also dying until stabilised.

Healing

• Stress heals at the end of each scene with time to rest.
• Injuries persist until treated — someone with Medicine skill can heal you.
• Defeat can be avoided by spending Fortune.

Magic in the Mythos

If your agent is a spellcaster, you have a Power rating and a tradition:

• Traditional — inherited folk magic (e.g. Celtic, Runeweaver). Uses Insight.
• Researcher — self-taught from forbidden tomes. Uses Reason. Powerful but dangerous.
• Dabbler — you stumbled into it. Uses Will. Flawed spells, limited knowledge.

Casting a Spell

1. Prepare your mantle at the start of a day (Diff 0 test) — hold spells up to your Power.
2. In combat: Prepare (minor action), then Cast a Spell (major action).
3. Roll the spell's skill test. Pay the cost (mental stress) after, whether you succeed or not.

Building Your Agent

Your agent — "agent" is the in-world term for a PC — is built from ABC + details:

Archetype

The core class. Pick one:

Background

What you did before the war: Academic, Athlete, Criminal, Entertainer, Journalist, Physician, Police, Spiritual Leader, etc. Shapes your skills and contacts.

Characteristic

A wildcard trait that marks you out: Bookworm, Dilettante, Dreamwalker, Street Kid, The Lucky One, Young at Heart… Often ties to how you got pulled into the Secret War.

Putting It Together

Pick an Archetype first. Add a Background — even an unexpected one. Add a Characteristic that contradicts or colours them. The interesting agents are the ones whose pieces don't obviously fit.

Truths & Name

Derive at least four truths from your ABC + nationality + language. Pick a name, a look, a voice, quirks. How does your agent move, talk, dress? What do they carry that they'd never lose?

Pregens

If your GM hands you a pregen — great. Read the truths and talents. Read the quotes. Picture the person. Then make them yours: give them a voice, a phrase, a habit. The sheet is a starting point, not a cage.

At The Table

Session Zero

Before you play, the group talks about tone, limits, and comfort. Achtung! Cthulhu involves WWII, cultists, body horror, and psychological dread. Not every table wants every topic. Be honest about what you want and don't.

Safety Tools

• Veils — content that happens "off-camera." Fade to black.
• Lines — topics that are completely off-limits.
• X-Card — tap the card (or a hand, or say "pause") to cut a scene. No justification needed.

Collaboration & Pulp Tone

Spotlight Etiquette

• Everyone gets a moment to shine. If you've been rolling all scene, toss the ball to someone else.
• Describe what your agent is doing, not just the mechanical result.
• Use Momentum for the team. Pay Threat sparingly but dramatically.
• When you roll a complication, volunteer what goes wrong. You know your agent best.

Quick Cheat Sheet