Pokémon X and Pokémon Y

I'm not sure how I feel about mega evolutions. Are they permanent? Like, when they mega-evolve, do they stay that way? o_o This is probably a dumb question since I just randomly popped in this thread after talking to someone about Pokemon all night.

Probably not given anime mewtwo changes between forms at will in the ova/film.

It's probably a hold item or you can change it between forms at a certain place.

edit: Serebii says it's a hold item.

- Pokémon can only Mega Evolve when they are holding a Mega Stone
- Blazikenite is not found within normal gameplay
- Mega Evolutions are temporary in battle
- not all Pokémon will have Mega Evolutions
- the Master Tower has a connection to Mega Evolutions
- stat increases confimed, with MegaLucario's Attack being higher
- MegaAbsol has increased Attack & Speed
- Super Training will increase Pokémon's "Kiso" Points
- next CoroCoro will feature new Pokémon, new Mega Evolutions and a type chart featuring the Fairy-type