Blood For Blood

2nd-level blood incantation

You inflict a minor wound on yourself in order to corrupt the blood of another living creature. As part of the same action with which you cast this spell, you cut into your own flesh, dealing 1d6 + 2 slashing or piercing damage to yourself. You then choose a target within range, which has to make a constitution saving throw.

On a failed save, the target takes 5d6 necrotic damage and cannot benefit from any healing until the start of your next turn. On a successful save, the target takes half the damage and does not suffer any additional effects. 

Blood for Blood has no effect on undead, constructs or other creatures that don’t have blood in their veins.