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Working on a generic 2d20 ruleset

I’m writing a series of blogs where i am breaking down the various 2d20 systems with the aim of making a 2d20 generic system, which you can mod with various add-ons.
First 3 are done:


Nice! I had been writing my own outline to help with working on a homebrew Stargate RPG. It’s very rough, more like an analysis and breakdown, and kept in a Scrivener project, but useful for my purposes.

So, a couple of details overlooked in your second post there, @Chriscdoa:

Personality is mainly folded into Will in A!C - or rather, Will covers force of personality. In addition, the need for a single dedicated “social” attribute was lessened by the second important detail:

In Achtung! Cthulhu, unlike MC3, Infinity, or Conan, skills have no default attribute. That technically means there are a total of 72 attribute-skill combinations (where Mutant Chronicles has lots of skills, but they only work with one attribute each), and means that, say, Fighting plays out differently when used with Brawn, or Coordination, or even Reason (meaning that we don’t need separate shoot and brawl skills).

As for the change in costs for extra dice… that came up in the Star Trek Adventures playtest, that it was too easy for a character to simply add 3 to Threat to buy maximum dice on a simple test, generate a lot of Momentum back, and basically start a sequence where the character could almost always guarantee rolling maximum dice. The escalating cost was the most straightforward fix to that, making each die after the first a more difficult choice, and it’s a design choice we’ve stuck with subsequently.

The system isn’t broken without that change, but I personally (as the guy designing and developing the core rules for most of these games) like the gameplay loop better with the escalating cost.


A!C GM guide out yesterday. Fallout out tomorrow (hopefully), and today the first part of my generic rules. Also included a link to the google doc, which looks nicer.

Thank you, I am looking to use the 2d20 system for my “dieselpunk” homebrew world. I think your work will help me for that, I already have the MC3 and conan books. what do you think about the ACHTUNG! CTHULHU rules compared to the others?

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I think A!C is pretty good. It’s simpler than MC3 and conan, and is the base i am working off for my generic set of rules. It also has Magic rules.

Part 2 - Basics

Part 3 - combat