Assassin's Promise

The price has been paid. The contract is made. The night falls, and so rises the blade.
You whisper a dark oath to a humanoid creature within range, promising their death. Whenever you inflict damage to the target, you can choose to place a later of a shadowy curse upon them. If the target dies before the end of the duration, you recover hit points equal to the number of layers you've applied to the target, and you 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 similat 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 effect.