There are multiple issues with this
>Magician needs you to have no item to use it
So you wouldn't even go into M-Hoopa or whatever
>Why would a Mega keep its base form's ability?
Stats and Abilities are the only 2 reasons megas are introduced. Why would they be so redundant.
However, it may not be a mega, but an alt. form, or may not use a stone, like Rayquaza. Who knows. And if this was bait, well fuck you then.