I don't know how many of you mewpoo players take advantage of this, but it's super awesome.
Essentially, you just let mewtwo's momentum carry him past your opponents shield with the b-air, so you hit with the thick part of his tail and you won't get grabbed. Chances are your opponent will unshield to either jump out with a b-air of his own, and that's when you jump cancel right into a f-air when you're behind them. It works so well for me, and I could be wrong, but this should be used way more often.
Essentially, you just let mewtwo's momentum carry him past your opponents shield with the b-air, so you hit with the thick part of his tail and you won't get grabbed. Chances are your opponent will unshield to either jump out with a b-air of his own, and that's when you jump cancel right into a f-air when you're behind them. It works so well for me, and I could be wrong, but this should be used way more often.