Thirsty Blade

You create a dark, ghostly blade of necrotic energy in your hand. Make a melee spell attack against a creature to assail it with your blade. On a hit, the target takes 1d8 necrotic damage, and it can't regain hit points until the start of your next turn.

If you hit an undead target, it also has disadvantage on attack rolls against you until the end of your next turn.

This spell's damage increases by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).