Round 1: Throw more needles, less approaching with up-smash, less approaching/retreating fair, more grabbing, less airdodging into the opponent.
If you throw more needles, he'll be pressured into approaching you, also its free damage for when he starts randomly throwing out d-tilts from half the map away.
Upsmash is slow, and the hitbox is small. iirc The first part hits on frame 11 and the second part frame 13. You shouldn't be hitting marth with this unless its as a punish for something super laggy. running in and upsmashing from a neutral position is pretty much bad against anyone. It can be nice if you predict a jump, but the majority of the time you're either going to eat a fair to the face, or hes going to shield it and punish you after it.
On your last stock you just started short hop fairing, for seemingly no reason. Hero would be nowhere near you... and you'd just throw out a fair, throw needles instead.
Punish Marth's landings with grabs, if you dash in and perfect shield Marth's fair while hes landing you have a free grab on him. Also don't down throw Marth, he's just going to DI it so hes facing you and suddenly you're in fair zone. If you B-throw Marth you have a guaranteed bair at mid percents, and high percents as well depending on how they DI. Also hes virtually helpless when hes in the air with his back turned to you like that.
Lastly don't airdodge into Marth, in general you're better off landing with an aerial than you would be airdodging into someone. If you feel the need to airdodge... do it away from him, or attempt to grab the ledge, just don't go directly into him, its a great way to give someone free damage on you.
Round 2: You're getting hit too much. Every time the game comes to a neutral position you just run straight at him and eat damage. It looks a lot like paddle ball, he hits you, then you rebound right back to him and he hits you again. Once again instead of running at him you should just throw needles, and if you must approach, you're better of walking and retaining all of your options than dashing.
Overall it felt like you just don't fully understand your move set. You would get into positions where you had an easy punish option, you just didn't know what to do. For example you'd spot dodge a shield breaker, then jab him at the furthest possible range, like he was so far away that you left yourself no followups to the jab, and ended up eating a fair. Another time he landed by fairing your shield and ending up right next to you, you could have grabbed or naired OoS, but instead you just kind of jumped away and let it go. That's just something that comes naturally with practice. Besides a few bad habits, I think what you need to work on most is getting a feel for Sheik.
