Cielre, Skybound Chimera

Mutate {4}{r}{g} (If you cast this spell for its mutate
cost, put it under or over target non-Human creature
you control. They mutate into the creature on top plus
all abilities from under it.)
Flying
Whenever this creature mutates, combine the
power of all creatures mutated onto it. (If you
had a 1/1 mutated on this creature, it would become a
5/5.)