okay here we go.
right off the bat...
Never allow yourself to be taken to Yoshi's Story against a Marth player
Ban it, every time. mewtwo needs room to move, and Marth literally controls the entire stage by simply existing (bar against shiek and the spacies). not that there are amazing stages for mewtwo in this MU, but Yoshi's is at the bottom of the list. try for Dreamland or FD next time (perhaps FoD?). the bigger the stage/blastzones the better
also the commentator literally made me LOL. it's at least a 70-30 MU in marth's favor (Maaaaaaaaybe 60-40 if you specialize in it like Taj, but even he has said he thinks it's worse even if it feels 60-40 to him). marth ***** mewtwo. no seriously
and i only have some general gameplay tips against marth, on a stage that isn't Yoshi's (lol)
stop trying to challenge marth with nair, or any of mewtwo's air moves for that matter. you should only be going into the air against marth if you're already comboing him. a perfectly spaced upair might be an exception, although i seem to recall marth being able to spike mewtwo's tail in the middle of the move. I'm not too sure about that tho
you need to work on your OoS game. SH teleport, wavedashing, even rolling will do you more favors than trying for a shield grab, or not moving at all. most marth's have a rythm to the way they play, and mewtwo is mobile enough to take advantage of said rythm. if he wiffs, get in there and make him eat some damage. if you can get the kill then go for it, if not then back off and try to reset in a way that will benefit you.
some BSBs will be very helpful for this, because when Marth's in the air, he'll either hit it, use his double jump, or eat some damage, most of the time if you react fast enough you can take advantage of the slight stun to hit him some more lol. that being said fight the urge to fully charge a Shadowball when fighting Marth (unless you're feeling brave lol); you need the smaller ones for weak zoning and tricksies, because it's the only move you have that has better reach than Marth
oh, and try not to let him get under you. and always try for the first port, it's the best one (I don't really remember where you spawn on Yoshi's tho)
even if the character beats mewtwo, you can beat the player.
Game two is your Ganondorf, not really a bad CP (Most marth's don't like the MU, i personally happen to like it a lot tho lol)
why did you go back to Yoshi's tho? >.<
only thing i notcied in that one is that your Lcancelling needs work
also @ commentator #2, don't nerf marth nerf the spacies
good job against the Doc, my only exp vs that character is as marth tho, no comments besides to try to learn to tilt the pills (about 90% sure you can do that)
So that's all i've got, sorry if it came across as preachy, i'm only average at putting my thoughts down as text.
do you travel at all? if you end up at one of the upcoming NE (MA) tournaments i'd gladly meet you and play against you. Smashachussetts would be best