I'm going to give scattered bits of information on the MUs that I feel aren't covered as well or are outdated concerning Derf's descriptions, as well as some stuff that's clearly my opinion but w/e (things like stages). By the way, I'm going to steal your highlighting too
DerfMidWest
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I'm not going to bother with spacies or Falcon much since the descriptions in the OP sum everything that you need to know up nicely. The only thing that's missing is that spacies love to CC shine and kill us from that.
Battlefield and Dreamland are your best bets. BF has perfect platform positions for movement, which you can use to approach him at different angles or camp. The platforms are also amazing for
extending combos from up throw. You can get things like up throw > up air > edge cancel dair (both hits) > nair > whatever (probably more nairs). Even more stuff can link if you're proficient at AI (aerial interrupt) nair. DL is like BF except Marth gets more room to move,
but Marth has an extremely hard time killing us. FD and PS are the next best stages. FD has large blastzones that you can use better and nothing gets in the way of juggling, but it also gives Marth a lot of room to abuse his better movement. PS is nice for the lower ceiling and the transformations can help us out (they give us more gimmicks than him) but we still don't have platforms that are of any use to us and he can use DB1 > up tilt to kill us faster.
Yoshi's Story and Fountain of Dreams are terrible. Avoid them like the plague. I have a definitive preference for YS though. There, we get scar jumps, a lower ceiling, and the platforms won't block our nair approaches. Why is it so bad? Tipper f smash kills us instantly and we have nowhere to run.
This MU is actually really similar to how Fox or Pikachu deal with Marth. In neutral, we can either whiff punish or call out his movement. Be sure to mix up where you place your nairs and how you go about baiting. Jolts are fairly useless, though if you have a lot of space or are in a position where there is minimal risk of punishment, you can throw one or two out to change the pace of the game, even though they should just be shielded or jabbed. I find myself able to do this most often on FD since platforms can usually get in the way. If Marth ever shields,
overshoot nair is unpunishable and Marth has no good options OoS behind him. If we're close enough, his nair will go right over Pichu's head, so you don't even have that to fear. Be careful if you land in front of him since up b OoS is fast and strong. That's all you have to worry about though, since
Marth's OoS options are all-around terrible.
We're not Pikachu, but our platform game is still quite stellar.
If Marth ever up tilts our shield, that's a free shield drop anything. We can also DD camp on the platform quite well if the Marth wants to approach since we can shield drop nair him if he gets close.
For edgeguarding, intercepting his up b with an
invincible nair works really well. You can also use jolts to push him back. If he gets hit, he's probably dead. You can also jump out and rising nair but this is risky and sometimes you'll just get hit by DB. If he's really low, you can do anything that prevents him from up b'ing to ledge-grab range since it's really easy to tech. Oh, and the Marth Killer is awesome. If he doesn't space up b well, you can down tilt him and go from there.
I'll definitely write some stuff up on Zelda, Sheik, Bowser and a few others later.