Mordenkainen's Lost Notebook

Retributive Enervation

7-level Necromancy

A creature which makes a melee attack against you must make a Constitution saving throw or take 3d8 necrotic damage. In addition, their hit point total is reduced by the amount of necrotic damage they take from retributive enervation. Hit points lost in this way cannot be regained by any means short of a wish spell until that creature finishes a long rest.