Grim Healer (5e Feat)
From D&D Wiki
Prerequisites: The ability to heal using a spell.
Learning how to use the more morbid side of healing you take advantage of it to sneak in wounds that someone would confuse to be an aid. Upon healing a target you can rather opt to have the target receive necrotic damage equal to the amount that would've been regained hit points. The target makes a Constitution saving throw against your spell save DC. The target takes full damage on a failure, and half damage on a success. You also have 5 charges in which can be used to add 1d6 additional damage to an attack under the previous effect, these charges regenerate after finishing a long rest.