Mega Evolution (Japanese: メガシンカ Mega Evolution) is a temporary transformation introduced in Generation VI that affects certain Pokémon. Mega-Evolved Pokémon are identified by having "Mega" in front of their name. There are 46 species of Pokémon that are capable of Mega Evolution, and there are 48 different Mega Evolutions.
A Mega Stone (Japanese: メガストーン Mega Stone) is a type of held item introduced in Pokémon X and Y that allows Pokémon to Mega Evolve. According to Professor Sycamore, Mega Stones are the results of Evolution stones being irradiated by the power of the Legendary Pokémon Xerneas or Yveltal.
A Key Stone is a small gem which is used to allow a Pokémon holding a Mega Stone to Mega Evolve. When the Key Stone is activated, the Pokémon's corresponding Mega Stone reacts to it, starting the Mega Evolution process. Trainers typically keep their Key Stone inside a personal accessory, although it can be anywhere so long as it's on their person.
During a battle, a Trainer can use their Key Stone to Mega Evolve a Pokémon that holds its corresponding Mega Stone before it attacks. Pokémon only remain Mega Evolved during battles and Pokémon Contest Spectaculars, and will revert to their original state once the battle has ended or if they faint. Every Pokémon that can undergo Mega Evolution has a corresponding Mega Stone that is named after it, except for Rayquaza, which instead needs to know the move Dragon Ascent to Mega Evolve. Some Pokémon have multiple different Mega Stones for their species.
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 Sky Drop. 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 Bestow, Covet, Fling, Thief, Trick, and Switcheroo will fail and the Abilities Magician, Pickpocket and Symbiosis will not activate. The move Knock Off 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 Embargo and Magic Room and the Ability Klutz 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 Sharpedo that normally has Speed Boost 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 Crunch that turn, it will be boosted by Strong Jaw, its Ability as Mega Sharpedo.
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 Sky Drop. 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 Bestow, Covet, Fling, Thief, Trick, and Switcheroo will fail and the Abilities Magician, Pickpocket and Symbiosis will not activate. The move Knock Off 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 Embargo and Magic Room and the Ability Klutz 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 Sharpedo that normally has Speed Boost 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 Crunch that turn, it will be boosted by Strong Jaw, its Ability as Mega Sharpedo.
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