Sorry about that. Try now
Yep, we're good now xD
Icebound said, you had great spacing going down here, and this match could have gone either way really. Since I fight a Ness main more regularly than most other MUs, hopefully I can provide you with as much info as possible for this fight:
- in terms of covering your landing, you do have to space your attacks so you hit with the tip or the sour spot for the longer shield stun. However, you should know that either FAir or BAir will end with a bit of landing lag, so that's a potential risk. You still have your SB (neutral B) or DB (side B) to cover your landing, as they carry through even if you're about to touch the ground. NAir is also a good option if spaced correctly, and the first hit is a setup move for your other attacks as well. Mixing it up will make your opponent wary of just running in to shield then grab. Another practice you can implement is footstooling your opponent if you know they are chasing you on stage. I know an Ike main that made excellent usage of this when he knows he's being chased into a landing trap.
- One mistake that seems to catch you a lot is your underestimation of when Ness can still attack in the air. Twice he nailed you with a landing BAir because you drop your shield/tried to roll and got caught at the starting frames of it. This is likely just getting use to the MU, but never expect Ness to be out of an option until he lands and be careful when you choose to roll. Here, it would help for you to go for out of shield options like grabbing or shield cancel jumping + DS (Up B). Those will serve you well against any character that does a single hit air attack.
- walking/running shield will be a saving grace in this MU, since the Ness was definitely trying to space you with PK fire. Thing with that move is that it is commitment heavy, so if you're able to perfect shield it or shield cancel jump after it connects, you'll be in great shape to press forward and apply more pressure to him. You don't want to give Ness the space to projectile spam, but at the same point, you can't allow Ness to pressure you from his air game. You have to make them feel like any option is not safe, and based on the previous iterations, Marth has the advantage due to him being able to outrange Ness on most close range encounters (he just might try to outspeed you is all).
- making use of your other options would help too I'd say. Your FAirs can be protected with a SB or DB (FAir assault in other words). FTilt and UTilt would assist more with anti air stuff, though judging from your movement, you already know this. It also wouldn't hurt to mix it up with a grab attempt here and there, since those set you up into more ideal positions for you rack up more damage.
+ Other than the FAirs, NAirs, and BAirs, your Marth playstyle is similar to mine, which is being passive aggressive. I could be wrong, but it seems you don't necessarily full agro your opponent, but you do leave baits to see which of the two your opponent will bite (whether they are agro or defensive) then you go in and make them pay for it. Understanding your own playstyle can help with figuring out what you need to do in the given situation.
+ I'll restate the point that your spacing was on point and the short hopping movement was excellent too. You did get hasty with your attacks, but that's something you've corrected yourself on. Fundamentals wise, your Marth is rather strong with that. Not much really needs to be changed in terms of what you do, just a few notes listed above that could press you in the direction you want to go with Marth. There are other setups and stuff that could help your playstyle, but that will be up to you to pick up or not, as it's not necessary with Marth to know for him to be successful I'd say.
Anyways, that's all I've got for now xD hopefully this will be of assistance to you.
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Have you tried approaching with Neutral B? He started adapting to you and shield grabbing a lot. For people that are spamming shield grab I usually jump and Neutral B. It's worth the risk because it'll cost them a stock.
I would be wary of using your SB to approach though, since that has a lot of commitment after the move is thrown. Its ok to mix it up with this option, but don't count on it all the time otherwise your opponent can just dodge through/perfect shield/counter past it. Trust me, I learned this the hard way xD