Zamudra, Apex of the Deep

Mutate {5}{w/b}{u}{u} (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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This creature is unblockable.
Whenever this creature mutates, each opponent discards a card from their hand, then exiles their graveyard.