Nethroi, Apex of Death is a mythic Legendary Creature — Cat Nightmare Beast card from Magic Online Promos (PRM), collector number 80905.
Mutate {4}{G/W}{B}{B} (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.) Deathtouch, lifelink Whenever this creature mutates, return any number of target creature cards with total power 10 or less from your graveyard to the battlefield.