Whyyy music? Game sounds are much better... they also help me figure out if there's something wrong with your wavedashing.
When you're recovering, you really should try to hit them off the ledge with a fair or even a Dancing Blade instead of the Dolphin Slash. You're unnecessarily cutting down your recovery options. Also, ledgestalling is your friend. Hanging on the ledge and waiting is a bad bad bad idea against Marth. Actually hanging around the ledge in general is a bad bad bad idea against Marth.
If fthrow to fthrow to grab didn't work the first time, it probably won't work the second time or third time either. Fthrow to regrab is pretty consistent so stick with that and don't waste grabs doing things you already know won't work.
At 0:35, you were both falling and too close to hit with both parts of the nair unless you doublejumped. A falling uair probably would've been the better option.
Okay, against Samus.
Maybe it's a personal pet peeve, but I really don't think using the Dancing Blade against floaty people is a good idea. But whatever works for you, I guess.
Your fair approaches are too high. Against most people, you will get shieldgrabbed.
When you ledgehop attacks like the fair, don't forget to fastfall or you'll get shieldgrabbed and thrown off again. I think you should try to ledgehop nairs more, though.
Your spacing is a little haphazard and could use a little bit of work. You're also fsmashing a lot more than I think is a good idea... you're not getting punished for it because... your opponent isn't very good, but you should be aware that there's a very high potential for punishment there.
...and jeez, sweetspot the ledge when you recover. Or at least ledgetech. Yeah, that's about all I can come up with right now.
