Warlock Pact Boon 1Dark One's Blessing
You instantly gain vitality from a cursed enemy when that enemy falls.
Free Action Personal
Prerequisite: Infernal Pact
Trigger: An enemy under your Warlock’s Curse is reduced to 0 hit points or fewer
Effect: You immediately gain temporary hit points equal to your level.
Published in Player's Handbook, page(s) 131.