Your enemies' attacks push you over a threshold, and you tap into a fresh reserve of strength. You unleash one of your ightiest attacks, fueled by your pain.

Daily  
Immediate Reaction      Personal

Trigger: An enemy bloodies you

Effect: You use one of your encounter attack powers against the triggering enemy. That power can already be expended, and if it is not, using it through this power doesn't expend it.

Published in Player's Handbook 2, page(s) 18.