Off the top of my head we have the advantage against Toon Link, WFT, Kirby, Bowser, Little Mac, DDD, Robin, Palutena, ROB, Shulk, and Samus. Mostly characters that aren't very good and either manage to also have lousy midrange options or in the case of Mac and Bowser are actually just really easy to edgeguard generally speaking because their recovery specials are really bad.
Then Mario goes relatively evenish with more characters, and loses to people that can space him out and edgeguard him consistently. Ganon and Link are the most obvious examples of characters that can do this reliably. Marth and Lucina are okay at it but don't always kill as early as the former two, though they got some major buffs so who knows. Ike gets bodied by Mario's juggles and actually still gets annoyed a lot by FLUDD edgeguards so he goes about evenish in spite of having pretty good tools in neutral against Mario. G&W beats Mario in spite of being mostly terrible because F-tilt spacing, U-smash juggles, and D-air edgeguards are actually really lame to deal with. The Pits have the best neutral game against Mario, are a a bit worse at edgeguarding him, but both can get KOs reliably with F-throw so they win by simply being consistent. Luigi in spite of supposed short range actually is pretty good at spacing against Mario because his Fireball, F-air, and Jab are all fast and generally have better range than Mario's stuff, which combined with his high damage is pretty lame.
Notably, most of the more spacing heavy characters aren't generally considered top tier, though Rosalina is probably a lot harder than most people give credit. Until you get the B-throw, she can wall and juggle Mario pretty disgustingly well.