Edit: It wasn't you, rewatching >>
Edit2: You have a pretty good marth.Here's what I saw
You have a really good edgeguarding game. But you can further improve it by using nair a bit more. It's a wonderful attack since even if they airdodge the first hit, the second hit will almost always kill them at decent %'s.(and it's fast as hell).
If you use a move that you just can't seem to get in, use a few other moves before you try again, less you be predictable. This sorta happened with dancing blades and you gave up after a few tries. You game is great right now, but it could be even better with a healthy diversity of moves =](we all love fair and bair, but marth has some other good moves too!)
Nice shieldbreaker, LOL. When I saw that shield drop I was just like, either that samus is gonna die soon, or that samus' shield is going to die soon followed by her death. xD
Oh and general tip, when the match starts against someone who uses projectiles, JUMP really fast. I find that when people face marth, they like to spam projectiles at the very start of the match to get in some quick damage. Even if they don't, it doesn't really put you in a bad position since it kinda already goes into your approaching fairs technique. =]
Good marth though! Keep working on that diversity of moves!
P.S. Dolphin slash out of shield at high %'s KILLS, and you rarely have to worry about decay killing the knockback since it's rarely used =]