Mega Evolution/Games/In Battle

In any battle, each Trainer may Mega Evolve a single Pokémon once. Mega Evolution is essentially a free action a Pokémon may make in addition to its normal move, but if a Pokémon will not use a move, it cannot Mega Evolve. Mega Evolution occurs before most actions except switching. A Mega-Evolved Pokémon will only revert to its original state if it faints or the battle ends; if it is switched out, it will remain Mega Evolved.

A Pokémon cannot Mega Evolve if it is being held in the airborne phase of. Neither volatile nor non-volatile status conditions such as paralysis, sleep, and infatuation will have any effect over a Pokémon's ability to Mega Evolve, even if they result in the Pokémon not being able to move that turn.

Mega Stones are not affected by most moves or Abilities. If they would move a Mega Stone to or from a Pokémon that could use it to Mega Evolve, the moves, , , , , and will fail and the Abilities ,  and  will not activate. The move cannot remove a Mega Stone from a Pokémon that can use it to Mega Evolve, and Knock Off's power will not be increased since it cannot remove the item. The moves and  and the Ability  will not prevent a Pokémon from using its respective Mega Stone to Mega Evolve.

Changes in a Pokémon's Ability will take place immediately. A that normally has  will not gain a boost in Speed at the end of the turn it Mega Evolves, but if it uses a biting move such as  that turn, it will be boosted by, its Ability as Mega Sharpedo.