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Normally you would not be allowed to cast Metamorphic Alteration targeting a non-Creature, because of its "Enchant creature" ability. But it could end up enchanting a card that is not normally a creature, due to an effect that makes it temporarily a creature, such as a a manland (Inkmoth Nexus). Or because it was enchanting a flip-walker (Jace, Vryn's Prodigy) that has now transformed.
So you turn Inkmoth into a creature, then enchant it with Metamorphic Alteration, making it a copy of Grizzly Bears. At the end of the turn, Inkmoth's ability wears off, so now you have Metamorphic Alteration enchanting just a land.
However, that land isn't a land, it is a creature still, because it is copying Grizzly Bears.
So does 704.5m apply here? Is this an Aura attached to an illegal object, thus causing the Aura to go to the graveyard? Or, is the object actually legal, because it is being made a creature?
704.5m If an Aura is attached to an illegal object or player, or is not attached to an object or player, that Aura is put into its owner’s graveyard.