Butchering Blade

You brandish the weapon or unarmed strike used in the spell’s casting and make a melee attack with it against one creature within the spell's range, otherwise the spell fails. On a hit, the target suffers the attack's normal effects, and necrotic energy seeps into the target widening and agravating it's wounds. If the target of the attack is missing any hit points they take 1d6 necrotic damage.

At higher levels: At 5th level, the melee attack deals an extra 1d6 necrotic damage to the target, and the additional necrotic damage increases to 2d6. Both damage rolls increase by 1d6 at 11th level (2d6 and 3d6) and again at 17th level (3d6 and 4d6).