Modiphius' 2d20 systems seem to commonly used some proprietary d6s for things like damage. I have access to three of the systems - Conan, Fallout, and Star Trek Adventures - and the d6s work the same in all three, so I suspect they're the same in most of their 2d20 games. The dice work as follows:
d6 Result | Symbol | Result |
---|---|---|
1 | * | 1 damage |
2 | ** | 2 damage |
3 | [blank] | 0 damage |
4 | [blank] | 0 damage |
5 | Effect Symbol | 1 dmg+effect |
6 | Effect Symbol | 1 dmg+effect |
In the system, various weapons and attacks can have 'Damage Effects,' such as 'Piercing 1,' which would ignore 1 point of damage reduction for each Effect symbol rolled. Any output would then need to total both the amount of damage rolled and the number of Effect symbols rolled.
Would that be doable at all?
EDIT: The Star Trek book calls them 'Challenge Dice,' but Conan and Fallout both call them 'Combat Dice,' so the latter might be the better name for them.