What's Sask? Anyway.
Match one.
Shielding against an aerial Peach probably isn't your best option. Float cancels basically allow her free hits on your shield, and Mewtwo is big enough for shieldstabbing to become a problem very quickly, especially against Peach's monstrous dsmash.
You're getting punished a lot for being greedy and trying to eke more charge out of the Shadow Ball. I wouldn't. Just throw uncharged ones to mess up the approach or possible make openings. It's not worth getting hit for over ten damage for possibly getting one or two extra damage in.
Your movement is a little lacking. For one, your Teleports don't look as well aimed as they should be, which just requires practice. I'll assume that you know not to hit the ground with it, but if you didn't, you do now. You're using wavedashes a little to evade, but it's mostly a single wavedash to shield or fsmash to try to counter an attack. Simple movements like that won't work at higher levels, so try to throw in dashdances every once in a while, and go from there.
You aren't using your tilts very much... which you should be. Really, it looks like you're using Shadow Balls at ranges where you should be grabbing or tilting. I'd look into that.
Woah, nice spike though.
I would recommend not messing around near the edge against Peach. Mewtwo's edgeguarding game isn't good enough to net him the kills on Peach that... say Marth could get, and you're really just restricting yourself to a smaller space, which means dsmash.
Try using dthrow against Peach at low/medium percents. You'll be more likely to combo out of that than anything... You could use the uthrow to keep her in the air, I suppose, but unless you're really good at that, it's not very viable. Also, you could try to land a fair or some kind of launcher after the dthrow for the same effect and be more assured in that.
Grab attack. Free damage. Mewtwo's throws aren't fast enough to throw anyone off the DI anyway. No pun intended.
Holy FUCK. Don't crouch cancel Peach's dsmash EVER. Just dtilt and let go of the Control Stick before she can whorenado you.
You're giving Peach too much wiggle room. Currently, she's calling all the shots and you're reacting. I guess it's working for you at the moment, but when you play better people, you should keep in mind that the proactive player always has the advantage over the reactive one.
If you're going to put in a song, at least make it cover the entire match <_<
Learn the uthrow killing percentages. Also, learn to DI better.