Vigilant Dead

You imbue a corpse within range with necrotic energy and create an undead guardian spirit The guardian hovers over the corpse, occupies that space and is invulnerable.

Any enemy that moves to a space within 10 feet of the guardian for the first time on a turn or starts its turn there makes a Dexterity saving throw, taking 10 Necrotic damage on a failed save or half as much damage on a successful one and their maximum hitpoints are reduced by the same amount until the creature takes a long rest. The guardian vanishes when it has dealt a total of 40 damage.