Abstract of Wildness

Trample, Ward—Sacrifice a creature.

Each non-Human creature card in your graveyard
has mutate and "You may cast this creature from
your graveyard using its mutate ability". The
mutate cost is equal to its mana cost. (If you cast
that 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.)