evenish:
bowser (Lol No. Grab Bowser: most of the top level Bowsers right now have Marth pinned at one of their bad MU's because of his grab game and how easy Bowser is to punish during tech chases. Bowser super armor literally doesn't come into play, and he can't keep trying to abuse Upb/safe mixups due to Marth's grab range and how fast he covers ground. Bowser is also prone slightly to juggling, but it's the grabbing that beats him.)
falcon (basically the same as the Melee MU)
dedede
spacies (Everyone but Wolf I agree. He probably beats Wolf)
ganon (I dunno about this one. He beat Ganon in Melee, the aerial Side B buff doesn't come into play that much. Marth swats Ganon at a range, he doesn't have to be up close to win.)
ike (2.1 Ike was a beast. This Ike I feel Marth beats: you win just about everywhere with speed. You have similar traits like sword long reach grab etc, but you tend to be faster and in general more mobile Side B not included. Edge guarding Ike got even easier, and Marth was already notable for being one of the few characters who could edge guard all of Ike's options reliably. Aether had to be sweetspotted or else he got a free tipper Fsmash, Dair still eats through Aether, Side B would also lose to Dair Fair Ftilt Counter etc.)
peach (I'd put it slightly Marth favor. Some of the unintentional buffs she got were changed back, like Dsmash with a turnip in hand.)
pit (I realllly think Marth beats Pit. Least 2.1 Pit. It is hard to run away from Marth, and up close he honestly gets pooped on.)
toon link (Strongly think Marth wins)
sheik (Same as Melee basically)
squirtle maybe (Def think Squirtle loses)
hard:
charizard (Grab. Grab big characters with Marth, and bad things happen.)
link (I think Marth wins, but I don't think Hylian agrees. Mid and close range, you should beat Link. Just don't get grabbed or combod with Boomerang, really bout it.)
lucario (I dunno. I pick Marth vs Lucario's on purpose and DD around waiting for them to approach. It was really awkward in 2.1 when all Lucario would do is DA in, because everything else was super unsafe. I dunno what all has changed with Lucario, but Marth has definitely been a safe character to pick vs Lucario so long as you make him do the approaching)
mario
ness (Ness eats it from Marth)
pikachu (Pika in general should be slightly disadvantaged)
sonic (arguable. 2.1 Sonic was rough and probably went even. New Sonic is a bit easier to deal with I think)
wrecks:
zelda
rob (Hell yeah. Rob gets pood on)
don't know everyone else