At-Will  
Free Action      Personal

Prerequisite: Elemental Pact

Trigger: An enemy under your Warlock's Curse is reduced to 0 hit points or fewer

Effect: The next enemy you place your Warlock's Curse on gains vulnerable 5 to the damage type matching your current elemental affinity. This vulnerability is cumulative with the enemy's existing vulnerability to the same damage type, if any, and lasts until the curse ends. The vulnerability increases to 10 at 11th level and 15 at 21st level.

Published in Heroes of the Elemental Chaos, page(s) 97.