BATTLE JOY
When you spill blood—yours or another's—and lose yourself in battle, you ignore fear, pain, mind-control, and the effects of debilities as long as you keep fighting.
When the action stops, roll +CON: on a 10+, that was a rush, regain 1d4 HP; on a 7-9, you're winded and out of it, but you'll be fine with a few minutes' rest; on a 6-, mark a debility but don't mark XP.