Assassin's Promise

You whisper a dark oath to a humanoid creature in range, promising their death. Whenever you inflict damage to the target, you can choose to place a layer of a shadowy curse upon them. If the target dies before the end of the duration, you recover hitpoints equal to the number of layers you've applied to the target, and gain a number of gold pieces equal to the sum of the target's ability score modifiers. If the creature still lives at the end of the duration, and the curse has not been removed using a remove curse spell or similar magic, the target takes 1d6 psychic damage for each layer applied. If you are dead, the target takes twice as much psychic damage and gains a level of exhaustion. 

The target is aware of the curse's effects.