Bloodletting

You touch a creature and expend 1 hit point, opening a wound where you touch. Make a melee spell attack against the target. You have advantage on the attack roll if the target is below half its hit point maximum. On a hit, the target takes 1d10 necrotic damage. If this damage reduces the target to 0 hit points, you gain temporary hit points equal to the damage dealt. These temporary hit points last for 1 minute.

The spell's damage increases by 1d10 when you reach 5th level (2d10), 11th level (3d10), and 17th level (4d10).