My gripe with the gameplay is actually his overusage of both spring offstage and of spring > dair in general.
Sonic has so many options for ledge guarding, and the fact that you consistently just used spring for every recovery option GIMR took just makes it that much harder to KO him when he realizes that that's all you're ever going to do to him.
The announcer's even chimed in on it. Sometimes, you're just so, so much better just
grabbing the ledge. Even if Marth makes it back on stage, he's vulnerable from upB landing lag long enough for you to waveland > smash or waveland > grab > bthrow to repeat the process. Ledgehogging is an exceptionally powerful tool vs. Marth. It only makes sense to abuse it to death.
I also think you could be a bit more liberal with your fair. It's a fast, decent ranged tool that can challenge Marth when spaced properly, and with the strong mixup game you have going on from what I saw in the videos, I feel like it could easily become a boon to your damage output.
Your output is the last big issue I think you might have. Even the commentary was joking about how little you were doing. I mean, damage is damage, but if you're putting in so much effort via movement and sideB/neutralB techs, then you should probably be getting more out of it than 1-3%. I think it's more of an opportunity to try out some higher end damage, especially on the front of the blast attack from the sideB itself. It does lead into some pretty effective setups, and at low percents, can combo into uair1, which gives you ample time for the dash attack > grab setup.
It's a bit nitpicky, but the last thing altogether that I'd suggest looking at is toning down is your flashiness. You had great opportunities for damage or pressure that you gave up for... whatever reason other than winning that you might have. Uthrow into jump behind them and downB confused the hell out of me because it was totally unnecessary. Uthrow fair or sweetspot nair, or even bair would've been far, far more effective with damage, setups, and landing pressure, all of which Sonic can abuse a character like Marth for exceptionally well. On some level, I feel like you should experiment with simpler setups just for the sake of taking some of that edge off. Playing flashy and fancy is nice and all, and it really catches the eye, but being that consistent for an entire tournament isn't gonna net you much when the game evolves more, and players start getting more consistent with the far more effective punishers.
Plus, given the way the meta's developing for the game (read: Not at all), picking easier options from things like an uthrow setup will keep that edge off when it comes to that consistent fanciness.
One thing that I will praise exceptionally is your movement. By god watching you cross him up over and over was beautiful. That's the kind of movement Sonic excels on, and its what makes him so incredibly difficult to hit and combo. If you trim back your spring > dair habit, it'll only improve from there.
Oh, and specifically against Marth, when its safe, it might be easier for you to cancel downBs with shield for the screech stop over jumping. Marth wins vs. Sonic when the Sonic is in the air, and that was your main means of getting out of the downB.
That's all I have to say about it. Keep that movement game up. It was sexy.
