Dirge Bat (Promo Pack) [Ikoria: Lair of Behemoths Promos]

Mutate 4BB (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Flash
Flying
Whenever this creature mutates, destroy target creature or planeswalker an opponent controls.