Snapdax, Apex of the Hunt

Mutate {2}{B/R}{W}{W} (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.) Double strike Whenever this creature mutates, it deals 4 damage to target creature or planeswalker an opponent controls and you gain 4 life.