Tuesday, January 7, 2020

Graded success for roll-under d20

This is a sort of half-baked add-on inspired by Call of Cthulhu 7e's graded difficulty system for roll-under d100 resolution. It assumes 3d6-based ability generation a la BX, and uses the same modifier scale, albeit towards a different end.

Basically, any ability score rated 3-18 has a "crit" range from 1 to (4 + ability modifier):*

Ability Score 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Crit threshold 1 2 3 4 5 6 7

You could also implement a simple skill system:

   Miss: Goes badly
   Success: Works, at a cost.
   Crit: Works
   Miss: Doesn't work - can push at risk
   Success: Works
   Crit: Works well
   Miss: Works at a cost
   Success: Works
   Crit: Works well

So what to do with all this? I dunno there's plenty of good games out there, play one of those instead. You're welcome.


  1. This is a cool idea, thanks! Very much appreciated by some one who is obsessed with d20 roll under attribute checks.

  2. Good stuff. It makes stats more important, but also has more "success at a cost" to make them less important?