If it enters as Flying type and changes type due to Mega Evolution, then it stays in battle. MegaZard X was already shown in a sky battle. Doduo and Dodrio are allowed because they're Flying type, it is gonna look pretty funny though lolWhat happens when Charizard enters a sky battle then MEvos to Charizard X? Maybe they have a criteria that allows Pokémon that at least look like they can levitate, to participate in sky battles? Doduo/Dodrio wouldn't be allowed in sky battles in this case.