I'll go with either 50:50 or 55:45 Mario's favor. I mean, it's iffy. Diddy gets comboed like mad by Mario but Mario is pretty susceptible to Banana. Pretty close MU either way.
I am not really aware of what other Marios think about this one. However, I would say it's 60:40 Mario's favor. Mario can easily get in on him and once Mario is in, Link isn't going to be in a very good situation. Link's bad mobility, weak recovery, and pretty bad frame data leave him vulnerable to all of Mario's tricks.
This one is 50:50. They both have insane frame data, both combo hard, and both are relatively fast. They fight similarly in a lot of ways and they can both KO each other pretty reliably.
I'm gonna go with 50:50 or 55:45 Mario's favor on this one. Fox's ultra fast fall speed means that Mario can combo him super hard and his linear recovery is easy for Mario to take advantage of. The thing is, Fox can also combo Mario quite hard and he has some more potent kill options (although they are less reliable) such as B-air.
Some say this is a losing MU for Mario. In my opinion, though, it's 50:50. I realize that Mewtwo outranges Mario with many of his moves and can escape his combos easily. However, Mario is very good at using Mewtwo's large hurtbox against him and the fact that U-smash kills him so early makes an already godlike move even more powerful in this MU.
60:40 Mario's favor. Roy is bad against Mario for the same reasons why he is simply a bad character all around. Awful sweetspots, fast fall speed, weak recovery, second worst aerial acceleration, etc.
This one is definitely 50:50. I happen to have a lot of experience with this MU. Corrin outranges Mario but has no combo breakers. They are just going to trade between Corrin getting a hit here or a hit there and keeping Mario at bay with his/her range and Mario getting in and racking up percent with combos that Corrin simply can't break free of.
I realize that I put a lot of emphasis on wether characters get comboed easily by Mario or not but it actually matters a ton. Comboing is a huge part of Mario as a character and if a character is very susceptible to that, then they will probably have a hard time with Mario.