If anyone who has Mewtwo in their game, then stay away from him. There is a glitch that causes him to use his custom moves (that are not released ... yet) if you view a Mii with certain customs, and another that causes there to be 10 of him in battle if you use him in any type of single player mode, which causes an automatic crash. (from what i have read, it happens on both versions)
Shoutouts to the Youtubers that told their fellow subscribers about it: EWNetwork, Games and Wario, GameXplain, just to name a few.