Also, Ampharos doesn't learn any dragon moves outside of Outrage from B2W2 tutors, so unless Amphy gets an attack boost, or they give it some new dragon moves in X/Y, it won't really be able to take advantage of it's new typing offensively.
Didn't the official site mentioned it will be getting Dragon Pluse?
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Depends. The effectiveness of a Mega-form Pokemon highly hinges on it's ability to perform in it's base stage.
MegaMawile may get one of the best abilities, good stat boosts and new good typing, but it's base form is still REALLY REALLY bad and likely to get one shotted. It needs a free turn to deal it's damage. Some Pokemon like Absol can get around it through things like Sucker Punch, but for Pokemon without priority, Mega forms may be difficult to pull off. If they resort to using things like Protect, it might be a way around things, but Protect has it's downsides too.
Ampharos as it stands doesn't typically force enemies out. While it's not really set up bait, it's not really amazing either. If it gets Parabolic Shock or whatever that draining Electric move is, it might gain more usage, as it will have a reliable way to heal itself. But there are a looooot of strong physical attackers in the metagame, and Electric by itself doesn't offer much in the way of resistances. The Dragon typing would help Ampharos' defense a lot, but it still needs to set up to get them. Setting up for defense isn't exactly a common strategy, and if Amphy DOESN'T get Parabolic, then it also loses leftovers recovery.
MegaAmph may end up going unused.
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