Demaro, Apex of Forget

Mutate {2}{w/u}{g}{g}(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.)
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Flying, Trample
Whenever this creature mutates, you gain life
equal to 10 plus the number of cards in
your hand.