Ever since we got the info today that activating mega evolution is done by simple activation that doesn't take up a turn, the one question I've had is: Why?
way i look at it possibly only one mega in a battle combined with being able to control when you mega evolve means you have to chose wisely when to mega evolve as to make the most of both your pre and post mega Evo abilities so it could add a bit of strategy
I could see a reconfiguration of stats. Lucario and Blaziken very much look like their power got over the top. I equate that to running berserk and thus lowering their defense stats even more(because not obeying would make them instantly useless and GF likely knows that).
i actually belive the reason for megaevolution to be able to activate and deactivated is simple, they already said you can only have one mega evolve at a time and in the demo deactivating use a turn so you can change your mega pokemon to another, lets say im in a double battle and i have two pokemon with mega stones, i activate one of them and the other one dont then if i see my opponent put another pokemon that is gonna beat my pokemon i deactivated it and activate the other pokemon. the other reason could be what people above me have already mentioned are good too, like lets say my ampharos becoming a dragon and the opponent change to a fairy then i deactivated my pokemon so it loose the dragon type loosing a turn but saving my butt.
Mega Evolution can only be done either once per battle or only have 1 available at a time, regardless, you may have other pokemon you want to mega evolve and making it automatic would not give you that chance to choose.
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Having it happen per choice can potentially make the 1 mega per team/battle works ALSO on the ingame/ special endgame non frontier facilities too because it could be actually coded and not related to the number of MegaStones on your inventory/pokemons holding it
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