>>20057185>tfw Banette would actually be usefulJust make them permanent, and if you still really wanted to be flashy, they could have a special entry animation to show that it's a Mega. Their Mega Stone would be infused with them or whatever and they'd be Megas in the overworld, they'd be Megas immediately as you send them in battle, and the only downside (though not really since it'd basically be the same) is that the stone still takes up their item slot.
However, the difference is that you now have turn one Megas. Some of them may want to hold off on this and you can just Mega Evolve them normally, like... Mawile wouldn't mind Intimidating then Mega Evolving, but sending out a Banette on turn one immediately Mega Evolved means that it can do some Prankster shenanigans right off the bat.
