Mega Evolution

Mega Evolution is a mechanic in the Pokémon series, introduced in Pokémon X and Y. It is a temporary evolution that can be initiated in battle if the pokémon is holding the mega stone for their species, however only select pokémon can undergo Mega Evolution. It can be triggered in battle before attacking, and it allows the pokémon to attack after undergoing Mega Evolution. Only one pokémon per team can be in its mega evolution, and after the battle is over any pokémon in their mega evolution return to their normal form.