Third Vid: Now this is a legit player. Pikachu definitely had the momentum for a good amount of the match.
-Too much dash attack especially when you were chasing him around. Replace your Dash attacks with N-air or RAR B-air. I also suggest (more like demand) you apply Running Shield(When you dash then cancel it by shielding) to your game to give you more ground options. I saw you do a few times but only to shield grab. You can apply any of your ground options in that manner.
-Speaking of chasing him around, you were doing a lot of that. Now initially there's nothing wrong with that, but that was how he was able to close the gap on you because you essentially kept running into **** (4:36 is a good example). 4:53 is when you started to apply the situation correctly. Keep doing that.
-MOAR U-SMASH! Pikachu lived for too long. At 130% U-Smash is an applicable kill move.
-You can cape Thunder (although Pikachu applied it pretty well this match) and you can FLUDD the Skull bash. You can also FLUDD his QA which would push him higher in the air and essentially make him a sitting duck.
-2:51 to 3:10 was a huge lulz moment on your part. You got way too caught up in Pikachu's momentum. There's nothing wrong with getting away from Pikachu when he's pressuring you so hard, but you didn't, and that's how you got damaged so hard and then gimped.
-The rolling was a bit excessive.
Fourth Vid: Mot much to say here. You handled yourself well.
-Though, you kept being a victim of his B-air, which was honestly spammed too much because it kept working. Up-B OOS completely ***** this, and it trades hits with your own B-air due to disjoints. I believe N-air works too, though someone needs to back me up on that one.
-Can't really stress enough on how you gotta apply U-Smash more for your kills.
-The Yoshi didn't pivot grab enough, which is pretty much his #1 move in his arsenal. For future reference, vertical spacing is needed when you meet a grab-happy Yoshi.
Last Vid: One where you finally lost. All right.
-Nice to see you finally contested Yoshi's B-air. Needed moar Up-B OOS though.
-For reference, 140% is when U-Smash kills Yoshi.
-About halfway in the fight you started to fall into your old habits where you run into ****. In general, you need to start shielding attacks more especially against Yoshi when he goes aerial. Up-B OOS is rather crucial for this to be beneficial to you. Contesting with B-air, U-tilt, and U-Smash works too, but yeah, Shield more.
Generally:
I noticed that you do not momentum break. This is actually very very bad as it's absolutely crucial to living longer. C-stick downwards when launched upwards to FF D-air which is our best MB vertically. Horizontally, you U-air twice, then either jump or fastfall to apply correctly there. I suggest saving your jump however. Your DI seems to be fine most of the time.
You have a problem with B-reversal fireballs when retreating. To negate this, drift backwards first, then put your control stick at neutral, then fireball. Similarly, you can fireball, wait till the fireball is fired, then drift back.
Get more used to spacing with B-air and jabs (yes, Jabs). It'll keep your opponent away when you don't want to be near them. All-around, D-Smash was overused when jabs were better.
More U-Smash.
Overall a legit Mario with plenty of potential. Needs some work, but who doesn't? Keep playing Mario. I'm interested in seeing how far you can go.