I haven't had much trouble with either Mewtwo, mostly because [i]especially [/I]Y is physically frail as crap. My Staraptor oneshots that thing to oblivion in most cases. 

I do agree that it's ridiculously powerful if it gets to start sweeping against an opponent with no priority though. It's pretty much gg at that point, unless you have a Sash/Sturdy or something else to keep you alive.