MTG Salvation

Wait... the other creature involved in mutate doesn't need to have mutate, right? I can place this card on top of Phage (who is not human) to give it flying, right? Sweet!

This is exactly the sort of value engine that mutate needs to mitigate the high concentration of materials in one space... unless an instant-speed kill in response to mutation blanks the new card like an aura...

Killing the creature in play before your card on the stack is able to Mutate onto it won't fizzle it. Instead, the card that was a "quasi-aura" will instead enter the battlefield as if you cast it as a creature.