Mega Pokemon Clause is a new Clause in CAP ASB XY, and the battlers can set the number of Mega Pokemon they want to allow in a battle. (E.G. No Megas, 1 Mega, Unlimited Megas etc.) Mega Pokemon Stones are linked to the Pokemon specifically and, like in-game, are not subject to any item removal or suppression effects such as Trick, Switcheroo, Embargo, or Magic Room. Knock Off does not get the power boost on a Pokemon holding a Mega Stone. In ASB, Mega Evolved Pokemon retain all of their base form's Abilities, and several Mega Pokemon that duplicate base form abilities have associated effects noted on their Mega Stone's Item Description. In Single Ability Battles, Mega Evolutions will have the ability of the Mega Evolution after Mega Evolving, but will retain any effects from the base form's ability (ex. a Moxie Pinsir that got an attack boost before Mega Evolving). If a Pokemon Mega-Evolves, it will use up one Mega slot, and the battler will be barred from further Mega Evolving if all Mega slots have been used up at that point in battle.
A Pokemon can Mega Evolve on any action in a round under any condition (Except before the first action of a round), including Sleep, Freeze, or Taunt. Mega Evolution must be tied to any single action, though it does not itself take up an action, and does not have an inherent Energy Cost (it may activate abilities that do, such as Drought or Sand Stream). Mega Evolution occurs before any other action takes place, regardless of priority (Pokemon will mega Evolve in the speed order of the Pokemon if multiple Pokemon are Mega Evolving). Mega Evolved Pokemon remain Mega Evolved for the duration of the battle once they have activated Mega Evolution, even if the Mega Evolved Pokemon fainted and is revived. Mega Evolved Pokemon will act with the speed priority they had prior to Mega Evolving on the Mega Evolution action, but will act with their updated Speed in subsequent actions. Their ability will be in effect immediately (eg. Mega Charizard Y summoning Drought), as will the updated accuracy boost if they have a +Spe nature.
Mega Evolution can be triggered when a battler posts his/her orders, specifying the action in which Mega Evolution takes place (eg. Thunderbolt > Thunderbolt > [Mega-Evolve] Outrage). Mega Evolution can be used as part of a Chance Substitution if the Pokemon has not yet Mega-Evolved. (eg. Charizard Mega Evolve A2 if X uses Rain Dance A1) (eg2. Gardevoir replace A1 with Encore, pushing back Mega Evolve and remaining action string if Y uses Endure A1)
