Bloodletting

You touch a creature and spend 1 hit point, opening a wound where you touch. Make a melee spell attack against the target. On a hit, the target takes 1d12 necrotic damage. If this damage reduces the target to 0 hit points, you gain temporary hit points equal to half the damage dealt. These temporary hit points last for up to 1 minute.

The spell's damage increases by 1d12 when you reach 5th level (2d12), 11th level (3d12), and 17th level(4d12).