Dead Gods Rising & Diesel Punk World at War
Once per round you may spend an action point for a class ability or to modify a d20 roll.
When modifying a d20 roll you must declare you are using the action point before the DM has announced if the action is a success or failure. An action point cannot be used when taking 10 or taking 20.
The character than rolls a d6 and adds the result to their original d20 roll and uses the new value.
At 8th level the character can roll 2d6 and take the highest roll, at 15th level they can roll 3d6 and take the highest result.
Dedicated Heroes can take the Faith talent and gain a bonus to their roll.
The Action Boost feat from d20 Future allows the use of d8s instead of d6s.