Bloodletting Bite

Necromancy cantrip
Casting time: 1 action
Range: Self (60-foot radius)
Target: One creature within 60 feet of you
Components: V, M (a weapon worth at least 1sp)
Duration: Instantaneous
Classes: Warlock
Subclasses:

You brandish the weapon used in the spell’s casting and make a weapon attack with it against one creature within 60 feet of you. On a hit, if the creature’s current hit points are more than half its maximum hit points, the target suffers the attack’s normal effects. If the creature’s current hit points are equal to or less than half of its maximum hit points, the target suffers the attack’s normal effects and takes an additional 1d12 necrotic damage.

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