Mega-Tar and Manectric I see having an impact on OU with Rain teams being so prevalent and their ability to mitigate that strategy a fair amount. in addition, M-Manectric has such powerful/fast offense in addition to a useful ability in Intimidate, that it can fit on any team that isn't meant for stall. Not to mention the single weakness to ground, as common as earthquake is, being a major plus.
Not as well versed in M-Ttar's outlook but it can run multiple sets, to varying degrees of success, even as a mega, though its DDance set is one of my personal favorites, which plays to its biggest strength as a devastating wall breaker.