[Let’s Study] Achtung! Cthulhu 2d20 Player’s Guide Part 2 Playing the game

With a setting with so much promise as Achtung! Cthulhu, you’ll definitely need a system that can keep up with the pulp goodness. 2d20 is a fair choice at this as it definitely isn’t a stranger to Pulp gaming as evidenced by Conan and John Carter.

But how is the 2d20 system configured for Achtung! Cthulhu?


Achtung! Cthulhu’s variant of the 2d20 system uses 2 kinds of dice: standard d20’s and Challenge Dice, which are essentially six-sided dice with a different pattern of sides, and is primarily used for inflicting stress in combat. These Challenge dice has four faces with three possible results: 1, 2 and effects, and two blanks.

There’s a handy chart in the book to help with this, but the dice available from Modiphius make this much easier.

Skill Tests

When a character rolls to perform something whose outcome is in doubt, then the player rolls a pool of d20’s against a target number determined by the acting character’s relevant Attribute+Skill. Each die that rolls under or equal to the target number is considered a success, and if there are enough successes to match the Difficulty set by the Gamemaster, then the player character succeeds.

Of course, there are some further considerations:

  • Dice that roll a 1 count as having rolled a critical success and those count as two successes
  • If the player character has a focus that applies to the Skill test, dice that roll equal to or less than the skill rating for the test count as double
  • Each die that rolls a 20 causes a Complication, which makes the situation worse somehow, and will be described in a moment

The system goes on to describe other mechanics such as assisting others in a task, as well as opposed and extended tests. Each of these permutations adds a little bit more complexity, but the core mechanic is still pretty straightforward.


Whenever a Skill Test result rolls more successes than necessary to pass the test, the extra successes are converted to a metagame resource called Momentum. This can be immediately spent on the test that generated it, or stowed away into a Momentum Pool that is shared among the player characters.

Momentum is a powerful resource that lends itself to many uses:

  • Buying D20s – before rolling for a Skill Test, a player may spend Momentum to add more dice to their pool to a maximum of 5d20
  • Create a Truth – a player may spend 2 Momentum to establish a new Truth in the scene or remove a negative Truth currently in play. The Truth created has to be related to the skill test passed and should logically follow from those actions
  • Obtain Information – the player may ask the gamemaster a single question that they must answer truthfully per momentum point spent. Again this question has to be related to the skill test attempted.
  • Reduce Time – Momentum can be spent to reduce the amount of time taken by a task.

Truths and Complications

Significant and impactful details relating to characters, locations and situations are identified in the mechanics as Truths. These take the form of one-word or short phrase descriptors that mechanically modify difficulties of certain tasks within a scene.

Complications on the other hand, are a form of Truth that acts as an obstacle that has a negative impact on the characters affected by it. It’s possible to buy off a Complication by spending Momentum (see “Create Truth” under Momentum spends above.)


In addition to Momentum, characters have a much rarer resource called Fortune, which can be used in several ways:

  • Critical Success – This sets a single d20 from a skill test to be attempted to automatically roll a 1
  • Reroll – Spending Fortune can be used to reroll any number of dice in a character’s dice pool (this applies to both d20’s or Challenge Dice!)
  • Additional Major Action – Let’s a player take an additional Major Action before anyone else has an opportunity to respond
  • Avoid Defeat – Spending a Fortune allows a character to return from defeat either immediately or sometime later in the scene
  • Make It Happen – A more powerful take on Create a Truth, this allows the player to introduce a new truth for the scene and can be used before rolling for a Skill Test.

Given how powerful Fortune is, it’s also a very heavily restricted resource. You can only spend 1 Fortune point per scene, and to regain it, you either have to refresh at the start of each adventure, or by doing something impressive in roleplay or achieving an objective.

Outside of that you can also voluntarily fail a skill test, or invoke a scar to produce a negative effect for your character in a scene to gain Fortune Points back.


The flipside to Momentum, Threat is a resource for the Gamemaster. They can spend it in similar ways to players but for use with the NPCs. The GM starts the game with a number of Threat depending on the number of players in the game, and can earn it in a few ways.

For players, attempting to ignore a complication from rolling a 20 during a skill test means generating 2 Threat for the GM. Performing a heroic but risky action also generates Threat. But the most common source of threat is from players buying additional d20s to roll in lieu of Momentum.

The 2d20 system has had a lot of experience for running pulp games so this variant for Achtung! Cthulhu fits the genre like an old glove. I like the Momentum and Threat mechanics and how it gamifies the expected see-sawing of heroics and danger in pulp fiction, while the Truths mechanics simplifies a whole lot of edge cases in a manner that is elegant in play.

Join me next time as we look into the combat mechanics!

For those interested in getting a copy of the books, you can get them over at the Modphius Website!

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