Yeah, you've got some work to do. I saw inconsistent shorthopping and it seemed like the time you full jumped there was no real reason. It wasn't terribly often, but it didn't redeem some of the other things in your game.
You didn't really ever tech. That's a problem. You shouldn't be missing as many techs as you are. You just don't need to. It seems like you just haven't learned to tech. Do that.
And although someone said that n-air is the best approach for Marth, I disagree. N-air is better than f-air as an approach, but it's harder to space and time as it has two parts to the attack. So if you want something you can pull out on command, f-air is the best bet. However, n-air is good as an approach when closing large distances, or so my experience has been. I'm not a professional Marth, so take what I say with a grain of salt, but I do have a bit more experience with him.
It seems like you're a decent smasher, but it's very obvious that you're not used to Marth.
You shouldn't be using Dolphin Slash onto the stage as was said earlier, but you did that several times. That just shows a lack of understanding of how to recover.
The only times you should be not sweetspotting the ledge are times when you need to. Sweetspotting isn't necessarily always the best option even though a lot of people make it out to be. There are lots of times when you have to land on the stage if you're playing against a good edgeguarder. Usually it's not as easy as just sweetspotting the ledge--they don't make it that easy for you.
Also, it seems like the aerials you're throwing are incredibly random. You'll just throw a u-air for the heck of it. Rely on f-airs, n-airs, and b-airs as your main arsenal for aerials. They are the ones you'll be using more often (in that order). U-airs and d-airs are more situational. You'll figure out more as you learn to play Marth when to use them.
I don't know everything about Marth, but it's clear you have a lot to work on.
One more thing, don't get cocky.
Yeah...you want to realize in the big picture how good you actually are. A good way to do that is to play someone near or at professional level. Let me tell you, it's a pretty humbling experience.
Anyway, let me end on a positive note: You are starting to learn how to use Marth, but you're only starting. Although you have a lot to work on, you are starting to get the hang of things. So my encouragement to you is this: Neither look at what you have and get cocky nor look at what you don't have and lose hope. What you want to do is see both at the same time and realize when you're making the gap between the two smaller. Be happy at the times when you are bridging the gap and disappointed in yourself when you're slacking in that. Aside from those times you should neither be satisfied or dissatisfied with where you are as Marth player.
Hope that helps and sorry if I was being harsh at all. I just want you to know what you can work on as opposed to keeping it a secret from you. And as everyone says, it's all experience. You'll learn more when you play Marth more. Oh, and check out videos of professionals and try to use some of their same techniques and incorporate them into your game. It can add another weapon in your arsenal that just may end up winning you a match.
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Bard