Momentum
A series of frustrating misses turn into a critical blow. Repeated fumbles while opening a lock turn into a nick-of-time success. Falling under a curse only to break free at the last moment.
Heroes are expected to fail occasionally. But it can get frustrating when heroes repeatedly fail at tasks they should normally succeed in, especially when they have invested time, resources and experience in specializing in a particular field. Eventually, things should work out in the heroes' favour.
Each time in a scene when you fail on a d20 roll, your momentum value increases by 1. Momentum cannot go above 5.
At a momentum of 1, the next time you roll a d20, you add on a d4 to that roll. Combine the result of both dice to determine your die roll for the purpose of the check.
If you fail a check while at a momentum of 1, your momentum increases to 2. At a momentum of 2, you add a d6 to your next d20 roll.
If you fail a check while at a momentum of 2, your momentum increases to 3. At a momentum of 3, you add a d8 to your next d20 roll.
If you fail a check while at a momentum of 3, your momentum increases to 4. At a momentum of 4, you add a d10 to your next d20 roll.
If you fail a check while at a momentum of 4, your momentum increases to 5. At a momentum of 5, you add a d12 to your next d20 roll.
If you fail a check while at a momentum of 5, your momentum remains at 5 until you succeed at a skill check or the scene ends.
If you succeed on a skill check when you have momentum, your momentum value becomes 0 until you next fail a check.
Your momentum lasts until the end of the scene. If the scene ends, and you still have momentum, your momentum immediately becomes 0 at the start of the next scene.
A GM may rule that checks that are particularly inconsequential or impossible are unable to generate momentum. For example, your character can't try and fail to hack into the US Federal Reserve from their cellphone to build up momentum to snipe a target, even if you really need to make that shot.