I'm not good at this game much/at all, but I can still offer advice in a third-party perspective. I'm just going to be typing this as I watch:
- L-cancel. I'm sure anyone who started watching noticed that considering the first thing shown was a FJ (or double-jump'd; idr) d-air that wasn't L-canceled. Shine after every aerial since Marths love to shield-grab. JC grab after shines, if they shield the shine, is great.
- Don't get too predictable. The wall-jump > side-B was a nice mind game and it worked twice, but try not to repeat things too much
- Marth is light so I'm pretty sure jab > u-smash works well. You tried it, but the smash followed up too late, I think.
- If you're going to hang on the ledge, do some stall stuff or at least drop down and jump back to get some invincibility frames.
- Try not to dash-attack too much; it's a great move, yeah, but doing it into a shield will lead into easy shield-grab. Most times, a SHFFL'd nair (when you can) is going to be as good as or better than a dash attack.
- Punish airdodges with smash attacks. P: You coulda easily killed when he had 140% or so.
- Needs more lasers. P:
- You don't always have to FireFox to the ledge. It makes it more predictable in any case.
- Wavedash more. I saw you roll right into a grab.
But I really liked your u-throw > u-airs early on and the edge-guard on Marth's second stock.
And most of these are small errors that might only occur just once; I'm just pointing them out as I see them. And just a reminder: stay off the platforms! D: I mean, you did a good job, but just reminding you.