'Kay, here we go, as I see it.
You're using the fair way too high, and you're not going to be able to inflict enough shieldstun to get away from being shieldgrabbed. Shffl so that you hit their shield at the last possible moment, it'll help you combo too. Also, don't use the shdf as an approach, and JC your grabs.
At 0:43 don't panic if someone grabs the edge before you, it's no big deal. Airdodge back onto the stage, fair them on the edge or at least recover low. You never want to Dolphin Slash that high.
And don't Counter.
Juggling is cool and all, but you shouldn't be waiting for them to get into the 140s. You should be going for the kill waaay earlier. Speaking of which, edgeguard Captain Falcon with the dair spike. It'll save you a lot of grief.
At 1:33, don't shy away from the edge. Ledge pressure is what Marth does best!
Don't use the Dancing Blade as an airguard. You're wasting one of your recovery options, and on top of that, it's not that good. Fairs and bairs are better if you're going for the stage spike.
At 2:58 I woulda gone for the spike, but it's your preference.
Mostly, just work on your shffl'ing and recovery. Your DI could use some work too.
I didn't really look at your Bowser match because... it's Bowser and no one really cares about him. You should learn to ledgestall better though, and again, don't use Counter and sweetspot better. Also... you should almost always be using the dthrow over the bthrow because... it's just better. Trust me on this one.
You're playing way too defensively against Falco. You're lucky he didn't just sit back and spam SHL at you. If you just sit there and shield or take the laser hits, there's nothing stopping him from just doing that until you're at a million damage. Well other than the fact that damage only goes up to 999. But seriously, too defensive.
You should also be more active in trying to edgeguard Falco instead of utilting him when you're close to the edge because he dies rather quickly.
I don't know if you noticed, but the Falco you were playing against shot rather high lasers. You probably could've gotten under them by dashing/crouching.
Oh yeah, speaking of dashing, don't dash attack. It's too punishable and predictable.
But yeah... that's about all I can think of/see for now. Hope that helps.