You are able to survive otherwise deadly injuries by supplementing your life force with arcane energy.
Prerequisite(s): Caster level 3rd or higher
Benefit: When an attack would reduce you to 0 or fewer hit points, you can instantly expend one of your spell slots for the day as a free action to reduce the damage. You suffer one less hit point of damage per spell level thus expended. The character may only do this once per day and cannot expend more than one spell slot at a time.
Undefeatable: The Collected Feats Sourcebook, Copyright 2009 – 2010, Louis Porter Jr. Design, Inc. Undefeated, Copyright 2011, Louis Porter Jr. Design, Inc.