Pokémon X and Y/Features/Mega Evolution

A unique state, Mega Evolution, was introduced in Pokémon X and Y. Mega Evolution is a temporary in-battle transformation that results in an overall increase in stats, sometimes also changing a Pokémon's Ability and types. Not all Pokémon can Mega Evolve. A Pokémon can only Mega Evolve if it is holding a Mega Stone in battle and its Trainer has a Key Stone.