Skylord! Some basics you should work on:
-landing grabs
-JC grabs
-wavelanding
-fairs
-edge game
-nairs
Those are some that come to mind after I watch some of your vids.
First things first - landing grabs. Against Falco, grabs are nice. You can bring him to 50% for free. Also, once you get him in a grab while he's in the CG percent range (up to about 30%), don't screw up! Know all of the tricks to getting out of it and make sure you see it coming. Use Utilt when he DIs a little bit away, and sometimes you can grab again after that. Be creative. That was off topic.. Anyways. With Marth's grab range, you shouldn't have to go too far to land grabs. Use waveshieldgrabs, wavegrabs, shieldgrabs, pivot grabs, and everything else in your arsenal. Again, be creative.
Wavelanding! I love this. Especially at platform stages, Marth's wavelands are underrated. If you're directly under a platform and Falco is in front of you and the platform, you can full hop -> waveland -> fair him into a grab. Or fsmash. Be creative.. again. Also, wavelands can mix up your edge game. Ledgehop into a waveland into a grab or Dtilt or shield or something else.
Edge game. This is importanttt. Thankfully, edgeguarding Falco isn't that hard if you know what you're doing. I saw you using Dtilts to edgeguard Oskurito, but not much else. Don't be afraid to use your counter on his UpB. If he's in the midst of charging his UpB, don't be afraid to drop off the ledge and reverse Dolphin Slash him, if you know how to do it. You can even drop off and hit him with a SideB, and his fastfalliness will do the rest. Almost anything will work. Also, since his UpB doesn't have much range, edgehogs are quite efficient.
Nairs! All I have to say about Nairs is that you use too many of them. You ledgehop into them, SHFFL them, and a lot of other stuff. I counted several opportunities where a tipped Fair or Uair would have been a better option than the Nair.
That's another thing! Surprisingly, a lot of people don't use this to their advantage - tipped Fairs send your opponents more upwards, and non-tipped Fairs send them horizontally. I love this.. you have so many options. It's great.
I happened to notice that you like to use Ftilt as well.. I don't know if it's just me, but I don't really like that move too much. Sure it has a nice range, but you don't need that extra range against Falco that much when all of Marth's other moves already have a decent range. I noticed a few opportunities where a well-timed Fsmash would have been better than Ftilt.
I'll have to think more about what else to say, but that's all for now. Also, sorry I didn't read your post, Arc, so I'm not sure if I repeated anything.
Good luck with Marth