When you imbue your weapon with arcane energy, you can expend necromantic power to drain the life energy from your targets.
Benefit: When you activate your Arcane Strike feat, you can expend an unused necromancy spell that you have prepared or a spell slot of a level in which you know at least one necromancy spell (for spontaneous casters). If you do, each time you successfully damage an opponent with an attack until your arcane strike ability ends on your next turn, you gain a number of temporary hit points equal to the level of the spell expended. This temporary hit points last for 1 minute per level of eldritch knight you possess.
Undefeatable: The Collected Feats Sourcebook, Copyright 2009 – 2010, Louis Porter Jr. Design, Inc. Undefeated, Copyright 2011, Louis Porter Jr. Design, Inc.