That match up isn't that hard though, it is all about sniping and doing math. The stadium game isn't hard to win if you run 4 Puzzles, which you probably should run. You can snipe their Shaymins/Hoopas with Yveltal BKT, Lysandring out the Hoopa late game to just be able to splash out some damage. Garbodor isn't a huge threat, your deck can snipe it while it is still a Trubbish, they also are going to be less willing to bench heavy due to Zoroark. Stand In also isn't the best ability (It is important, but not the best), Fright Night is going to win you the match up most of the time. The easiest way to deal with Mega Mewtwo itself is keep countering the Stadium, and make them over invest into a Mega Mewtwo and punish their one attacker, generally once you get through 1 the match is pretty much over. They also aren't going to have the Stadium, 2 Psychic Energy + DCE, and Garbodor all the time. Currently, I have a win rate of 60% towards Mega Mewtwo, after 20 games being played, this isn't to say it is an easy matchup, but it is definitely winnable.
Mega Scizor is pretty original, and it wins against Mega Ray and Mega Mewtwo, but once you hit anything rogue, you will probably lose.