De-Evolve

Target mutated creature is separated into two
creatures. Whatever creature was on top is
separated along with any equipment, auras,
counters, etc. This new creature is the target of
any spells or effects currently on the stack that
target the original target of this spell. If more
than one other creature was mutated with the
target, you may arrange them in any order.
This spell's effect counts as mutating.