Bloodletter's Curse

Unique – Vile Decay: Dealing magic damage to an enemy champion with your innate ability or abilities applies a stack to them for 6 seconds, stacking up to 6 times and up to once per basic attack or ability per cast instance every 0.3 seconds. Each stack inflicts 5% magic resistance reduction, up to 30% at 6 stacks.

Limited to 1 Blight item.