From Edge of Darkness Wiki
Banishers p. 41
Character Creation Only
The mage can expose her body to the raw power of the Supernal Realms, opening a more potent channel for the energies of improvised spells. If she willingly suffers up to as many points of resistant bashing damage as the lower of her Resolve or Composure, she can add dice equal to the damage she suffered to the pool of one instant, improvised spell, cast at the time of the injury.
Alternatively, she can suffer resistant lethal damage to enhance improvised extended spells. Once again, she can only suffer as much resistant lethal damage (and add as many dice) as the lower of her Resolve and Composure. She must suffer these injuries for each dice roll — not once for the entire casting.
Body-Ravaging Magic manifests differently for every Banisher. Some suffer spontaneous burns, cuts and contusions. Classic stigmata and spiral burns over the chakras have been reported. Others cough or cry blood, or simply tremble and turn pale.
Drawback: Injuries and limitations aside, this Merit can’t add dice to rote versions of a spell.