Ikoria's new Mutate ability allows two or more creature cards to be fused into a single creature, with the creature on top gaining the abilities of the creature cards below it.
From a rules perspective, what exactly are the non-top cards? While they wouldn't be considered creatures in their own right, are they still considered permanents? Are they still targetable? Do they count as being on the battlefield?
I'm primarily curious about two specific edge cases:
- Is it valid to play a "Destroy target nonland permanent" targeting a non-top mutate creature card? If so, would the entire mutated creature be destroyed or would the targeted creature card be effectively removed from the mutation?
- If a Legendary creature card is a non-top card in a mutation, is a Legendary with that name still considered to be on the battlefield for the purposes of casting a second Legendary with the same name? If it still counts as being on the battlefield, what happens when the second Legendary is played and you choose to get rid of the first one? (I suppose that partially boils down to the above question as well.)
As the official rules haven't yet been released (to my knowledge), I'm aware that some of these questions may be difficult to answer. However, there may already exist related or similar rules/mechanics (that I'm not aware of) that already provide a clear answer to such situations. Any relevant quotes from Wizards employees may also shed some light on the subject.