Valaista, Elemental Scion

Mutate {3}{w/u}{u}{r}(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.)
Flying, Flash, Haste
Whenever Valaista, Elemental Scion mutates,
enters the battlefield, or attacks, nonland
noncreature cards in your graveyard gain
Retrace until end of turn.