Draning Kiss

Your lips become a siphon to suck the life force out of your opponent. You make a melee spell attack, against a creature. On a hit the target takes 1d4 necrotic damage. When the target takes damage they have their hit point maximum reduced by half of the damage dealt, and you heal that much. This reduction lasts for an hour. The target dies if this effect reduces its maximum hit points to zero.

This spells damage increases by 1d4 when you reach 5th level (2d4),  11th level (3d4) and 17th level (4d4).