I'm thinking about implementing the following houserules at my table to try to bring back the concept of "Critical Successes" by piggybacking off the Advantage/Disadvantage system.
Whenever a creature makes a d20 roll with advantage, if both dice in the advantage roll result in a natural 20, then something especially good will happen as a consequence, determined at the DM's discretion. For an attack roll, this might mean increased damage on the critical hit, or for a Saving Throw, it might mean avoiding all damage from a spell that normally only reduces to half.
Conversely, when a creature makes a d20 roll with disadvantage, if both dice in the disadvantage roll result in a natural 1, then something especially bad will happen as a consequence, determined at the DM's discretion. For an attack roll, this might mean dropping their weapon or causing a self-inflicted injury. For a Saving Throw, it might mean suffering an additional effect contextual to the spell/source.
Although unlikely, if a "Critical Success" occurs in a scenario where success is normally impossible (like a creature with +3 to Charisma making a check with Advantage against a DC of 24), a "Critical Success" should not result in the check succeeding; but it should confer some kind of nominal benefit that reduces the penalty of failure or offers a different path forwards. Conversely, "Critical Failures" should not cause a check to fail if the total still matches the DC (like a +9 check with Disadvantage against a DC of 10) but should confer some nominal penalty to the result.
There's a few things I'm trying to do with this rule:
- I like the idea of "Critical Successes"/"Critical Failures" as a ludonarrative mechanism for especially unusual outcomes to gameplay situations,
- But I don't like the high frequency of these outcomes when using traditional "Critical Success on 20, Critical Failure on 1" rules
- I also like the idea of Advantage giving a small chance of an especially good outcome occurring, with a reflective chance for Disadvantage for something especially bad occurring.
Has anyone attempted to use a rule like this in their games? If so, have players enjoyed this adjustment to the d20 rules? I worry that as-written the rule might be too insignificant to really affect gameplay, is that a potential issue? Should I flesh out the potential outcomes that can occur when following this rule?