First thing I see is that you're throwing out the fsmash way way way too much. It seems like it's your go to move. Well, you're not Bowser, and fsmash is not your Fortress =P If you'll notice, pretty much every time you whiff a dtilt, you immediately go for the fsmash, on the stage or on the edge guard. You're not getting punished for it (which is weird) but you're missing a lot of opportunities.
If you hit their shield with a dtilt, don't panic! It's not that easy to punish, so just wait and see what they do and react to that, instead of hoping that they'll drop their shield and eat your fsmash. If you whiff the dtilt edge guard, don't add to your problem and use an even laggier move. Another dtilt works just fine, or a jab or something. Fsmash is a good edge guard, but it isn't the alpha and omega of edge guards. Consider using smaller, faster attacks that'll put them in a less variable position that you can take advantage of, because faster attacks mean more opportunities. Does that make sense?
Also, don't be afraid of going off the stage to edge guard. Foxes these days are tricky and mix up their Fire Fox angles. And generally, they've got three or four different ones they can pick, so it's hard to cover them all, especially considering they can shoot high and drift to bait out your attacks. Instead, choke them off early, when they don't have nearly as many options.
You're way too careless on the recovery. You can see it from the very first time you get knocked off, match one. Your double jump takes you too high when you're grabbing the ledge. No, you didn't get punished for it, but you could've. Other times, you're going straight into bair or shine range on your recovery when you absolutely do not need to.
Yes, you can cover your recovery with the fair. But that doesn't mean it's entirely safe. If you trade hits with Fox's bair, he gets knocked back onto the stage and you die. That's all there is to it. Use fair to dislodge them from the edge, don't expect to slash through every edge guard from every other character. Marth's good, but he's not that good.
Your playstyle is really different. Which is cool, uniqueness is good. But the traditional things Marth does are traditional for a reason. If you grab them near the edge, tech chase. It's reliable damage that potentially sets up edge guards and kills. Don't dsmash randomly and ruin that all. Even if it connects, you're not getting as much out of it as you could be.
If you grab them in the center of the stage, uthrow and do the chaingrab for damage. It's guaranteed damage, and when they land on a platform, you can hit them with utilts or fsmashes. There's absolutely no reason to throw that away and try for a possible flubbed DI to get a single fsmash in.
Uh, yeah, that's all for now.