"Start of match"
Unless you knew this ZSS throws away all but one piece at the start, you shouldn't have started with a sh fair. Fair only gives you 4 frames, while shffl airdodge -> shield (12 frames of vulnerability) or dash to shield (17 frames of vulnerability but a huge distance cut down) of safety compared to fairs 20+ vulnerability it was a slightly silly move that could have had two pieces thrown at you, the second being glide tossed for easy damage to the ZSS before the match even started.
0:10 - You go for some fair/gimp off stage, ZSS isn't going to get gimped at this low percent, but you left behind an armor piece, which... well, could have gimped him if thrown appropriately. Also watch out for the vertical spacing, you could have hit with fair if you fast falled.
0:18 - You grab the armor piece again but let the ZSS get back to the stage with much ease. I know you wanted to chuck the thing again, but you were close enough to punish with db (13%+ instead of 10%) and then could have followed up with a chucked armor piece for more percent.
~ Plus I'm not sure why you glide toss back both times?
0:36 - It was very easy to see that ZSS was looking for an above stage recovery, the dtilt wasn't needed, as a reflex action less than a second later would have been better. Plus after ZSS goes above you, you shield, a bad habit perhaps? ZSS hadn't of started a down b, so up air strings would have been perfect here.
0:38 - Badly spaced fair on shield for no real good reason?
0:40 - After the throw you start aiming for a space as if a ZSS would challenge you in the air horizontally. Plus you jumped; at this point of time, the ZSS had full view of Marth's glaring weakness of below him.
0:44 - Full hop fair? Is this a habit of your opponent's you're trying to punish?
0:52 - Instead of going for a fair, you could have done better (at least better than not punishing the tech roll at all) with nair, or with slightly more patience an uair as well. Lack of patience cost you a grand opportunity for a kill. And you then get punished for it too.
1:10 - Just like I, I love spamming aerials after a kill, but once ZSS is back, you need to quickly reinstate zoning, which you didn't do, allowing ZSS to properly abuse her invincbility frames to hit you.
Protip: Being too close to the ledge forces you off it, and you lose your shield as well very easily. You stalled within your shield for whatever reason, even though ZSS wasn't within your inner red zone. You could have waited for the platform above to return for safe passage back on stage, or reacted faster to beat out the ZSS.
1:17 - This was completely avoidable. Even with the bad timing so that you didnt sweet spot, I think you may have been able to just di forward onto the stage 'just'.
1:20 - You start your stock going for a grab, easily predicted by the ZSS. Whilst avoiding the grab, at 1:22, ZSS put herself in quite a bad position for punishment (probably far exceeding the 24% you would have gotten for fthrow fsmash).
1:27 - The ZSS has shown so far to mostly recover above the stage (ledge jumps included), ignoring this has so far made you lose out on many opportunities.
1:36 - Players will generally always roll or jump when backed into a stage ledge, it was possible to punish.
1:50 - Eep at getting hit by ZSS's dair ;\ Uair would have done fine...
2:15 - You could have gone for the platform after your up b, no?
2:19 - FFing closer to ZSS after escaping her dsmash could have turned out a lot worse...
2:21 - A fast fall to utilt/upsmash would have most likely worked here. The ZSS air dodged prematurely, noticing this you could have gotten the uair.
2:26 - Cr4sh doesn't seem to dash attack except as a visible punishment (like when you sh too close), yet you space yourself predicting one quite a bit (or a side b); ZSS getting grabs is something I thought to be quite rare...
2:32 - This lack of sweet spotting is DANGEROUS.
2:45 - I think one of your biggest weaknesses is the lack of patience, and you often aiming your sword at places where the ZSS hasn't even shown signs of going to yet... ZSS is punishing badly spaced aggression via dash attacking your short hops.
2:56 - In the spam of 20 seconds ZSS has punished the sh attempts with dash attack like what? 4 times?
3:20 - And once you're at the right percent, punish that short hop with side b for the kill. Zing.
3:31 - Fairs aren't always your best approach, yet you were baited into the dsmash not ONCE, but TWICE (fool me once shame on you, fool me twice...) You going for an uair would have been completely safe, and probably would have killed. Knowing he was about to lose a stock, since he put himself in a bad position, him getting 38% out of it is horrible.
3:38 - I know you're going for that 24% here, and so does the ZSS. She has just left herself wide open, and I'll tell you something, ffuair to upsmash is also a combo at 0% and does 34%. Hell, the reason we go for the fthrow fsmash is because it's a punisher of opponents avoiding our other CRAZY **** we have at 0%.
3:44 - Dash attack to punish sh.
3:47 - Repeat above.
3:48 - ZSS must not think much of you to try for a third time in 4 seconds. Thank god you punished here.
3:53 - Uair <3. Jab was an accident though, right?
3:58+ - You're letting yourself get juggled here by trying to get behind/through ZSS. there's a nice sexy platform safely waiting for you below, or a nice safe ledge because you haven't dolphin slashed as well. Now you lose your jump and are more suspectable to juggling.
4:01 - You're FALLING TOWARDS ZSS from above her. See the problem here? Luckily you air dodged through it :D
Over all I'm seeing a bit of "memory'd" play at the moment, instead of a reactive one. Realising that things like shield can be left to the last moments (comes out in 1 frame) or awaiting to see what your opponent does when they are in a bad position instead of trying to predict wrongly and fail... Is something you need to work out.
Also your own predictability and how predictable cr4sh was in outsting you for it was pretty painful. How many times would have a retreating sh/shff shield saved you and allowed you to punish BEFORE you get into kill percents and ZSS starts spamming side b to finish you off while you're trying to short hop?
I'm going to be a lot more brief for the second match, as I'm pretty sure I covered a lot of your issues already.
Match 2!
4:22 - So it is a habit. Every habit on everyone not using meta knight is punishable.
4:37 - Much better vertical spacing. How awesome are 'empty' aerials covering where ZSS could only hit you with a jump of her own (and not win) to a fast fall punish!? :D
4:47 - Work on only doing one side b. There's 22 frames of hitstun after the first hit (14 if they're in the air), you have the time to chill if you miss the first hit as to not get punished by the roll.
6:00 - Getting better at avoiding the really simple punishment ZSS has on your short hops. Slip ups are a-okay.
7:18 - I noticed this towards the end of the first match, instead of always ledge jumping, ZSS started to mostly do get up attacks. The shift was possible to note much earlier.
7:34 - Hold it for a moment there MISTER. Did I just see what I thought you did? You gave up a perfect position, especially against ZSS by allowing her to just dash under you? WAH!? You had complete control, and a bit of patience would have followed with opportunities as ZSS 'struggles' to get past the unfavourable position.
Over all my end of match 1 comment applies. Your Marth is good, you know how he works, HOWEVER, your biggest weakness is the lack of patience. Being patient doesn't mean going slower, it means not doing anything stupid/punishable in a moment that should have been the other way around.
Sorry if I'm overly harsh, I do that, but I definitely liked watching your Marth.