« Weapons and armour | Basic Roleplaying Rules Repository | Determinating Critical Successes »

The effect of rolling doubles

Game System: Basic Roleplaying
Author: Bruce Mason
Added: 2006–09–16


Whenever a character rolls double on percentile dice as part of a skills test then the result is significantly better or worse than usual. The usual effect of rolling a double is to gain a critical success or to suffer a fumble. This rule replaces the normal critical, special and/or fumble rules.


“Rolling a double” refers to any percentile roll with matching 10′s and units dice. The doubles are: 11, 22, 33, 44, 55, 66, 77, 88, 99, 00. In addition, the result “01″ counts as a double.

  • Whenever you roll a double and fail a skill test you have “fumbled” and the result of the roll is “twice as bad as normal”.
  • Whenever you roll a double and succeed at a skill test, you have “criticalled” and the result is “twice as good as normal”.
  • The numbers 01 and 00 are “special doubles.” 00 is always the worst possible double result. “01″ is always the best possible double result.

Doubles and skills over 100.

If BRP or the BRP-based system you are using allows skills over 100% then some means of increasing your critical chance is needed. Various possibilities exist. E.g. if your skill% is over 100 then treat the excess over 100% as a critical threshold. E.g. if your skill is 125% and you roll 17 then your critical threshold is 25% so the roll of 17 is a critical.

Effects on other rules

These rules replace any critical/special and fumble rules in action.

Play notes

I have used this system in Call of Cthulhu and RQ3 and will use it in Mongoose RQ. I recommend that is used in conjunction with these other rules which I will add later:

This is also a test for me at playing with this wiki.