PPMax

When you say it goes back to normal, is it random or guarenteed? For example, if I were to just leave the Mega in my party and not do anything with it, would it still revert at some point? Also, if you use them in Amie, does it show the model of the Mega Pokémon or the standard form?

Will the Mega Pokémon be usable in Pokémon Amie?

I have noticed that you can make Pokémon files in their Mega form with PKHeX, but I was wondering if that could screw up your game. Would this also allow you to double Mega Evolve with Charizard and Mewtwo like I have seen in some videos?