Vincenzo's Vengence

With a whisper of a vitriolic phrase chosen by the caster, An aura of necrotic energy sprouts forth from your wound and envelops the attacker in a harmful necrotic shroud with power equal to that of the damage done to the caster. The target must make a constitution saving throw, on a fail the target takes the same damage dealt to the caster as necrotic damage or half as much damage on a save.