I'll start with Mario since he's Nintendo's mascot. Played a lot of Mario's on ND so i got experience on other stages outside of FD.
Will edit this post soon. Gotta start from somewhere.
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vs
Pros: Because MK uses a sword he literally beats every single aerial in Mario's arsenal, this gives MK a huge edge in racking up damage and snagging a kill(only if the player is foolish enough to challenge MK with their Dair or FF nair). For example MK's up tilt beats anything Mario has to offer above MK so this gives us the ability to reset Uair chains, also edge guarding Mario is much easier as he'll be helpless against MK off stage. Moves such as Nair or Bair beat Super Jump Punch if timed correctly.
M-Nado is good to
abuse if Mario is all up in your face, if you want to be safe using Dtilt will push Mario away and can set up for a dash attack depending if the player reacts to the fast Dtilt. Dtilt has a 25% chance of tripping so it'll sometimes give you a guarantee dash attack which can lead to combo's OR at high percent lead to a solid kill: Dash attack ---> SH Shuttle Loop.
MK recovery options shouldn't lead to you getting spiked by Mario's Fair, we can recover low to prevent his Fair from ever connecting, we can recover using Dimensional Cape , Side Special into the ledge etc.
Best place for Mario to be for us is near the ledge, M-Nado covers so many options. Their only bet is to get up attack but spacing and good reads is key, if you're really smart you can get a F-Smash read but i would recommend playing it safe by using M-Nado.
Despite how people make fun of MK range calling it a 'butter knife' or 'toothpick' his range is actually better than Mario's and as i said earlier MK sword counts as a disjointed hitbox.
Cons: Mario does not need much commitment or air dodge reads to rack up the same if not more damage than us. From 0% all he needs is a grab and then proceed to string Utilt, when i got caught by a friend the other day by this combo i couldn't break away MK fastest aerial is Dair but i couldn't break out but when i finally could he ended the string with an Up Smash leaving me with 46%. After this percentage we don't need to worry about dangerous combo's like that but sadly he can Super Jump Punch out of D-throw
even at high percent.
Not only is his combo's easy to do and give high reward but his Up-Smash beats out aerials, the usual camping above opponents while flinging out Dairs then falling with a Dair or M-Nado are invalid and are dangerous to do because Mario's head during U-Smash is invincible. Moreover his Up-Smash can beat out our Dimensional Cape when used as an attack, this is the most dangerous move and will most probably snag the most kills due to MK being a light weight which means he lacks vertical resistance. So try not to DC Mario while he's charging an Up Smash because he'll win.
D-Smash comes out almost as fast as ours and like ours packs more of a punch on the 2nd hit, this can lead to a hard punish if we try to mix up our landings in a helpless state. This also why i don't like FD because Mario's immense ground speed allows him to punish us with pretty much anything, say for example after using M-Nado Mario shields you drift away but Mario chases you and grabs you. Characters like Kirby wouldn't be a problem but Mario can easily punish us if we make mistakes like that.
Other Stuff: Mario's fireballs are not a threat because MK has the most jumps in the game, abuse this if they decide to pressure you with F balls they'll have no choice but to approach and change up their game. M-Nado and Side Special beats F-Balls too i would recommend using M-Nado in mid range, not only will Mario not be able to react but you'll also dish out more damage minimum being 15% if mashed well enough(Side special shouldn't be used at all offensively it isn't safe).
Stages: Our recovery options are flexible thanks to Dimensional Cape, stages such as Smashville,Battlefield,Town and City are perfect for MK. Not only can he ignore F-Balls easier due to platforms but also use platforms to avoid punishment after M-Nado's ending lag and use Dimensional Cape onto a platform the Mario player won't expect. Any stage with platforms will benefit MK greatly.
My Thoughts: I think the match up is even or at least slightly in our favor, weakness such as Mario being below us and his U-Smash beating anything we throw out can be avoided by mixing up landings. You can stall in the air with your jumps, use Dimensional cape onto the stage but far enough so the Mario player won't punish, head straight for the ledge, etc. Keep them guessing.
Despite Mario's insane Down throw combo from 0-45% we can also dish out damage by baiting air dodges and getting the most out of our Dash attacks and Down throws. Down throw into Shuttle loop = 22% and in mid percents Down throw to M-Nado gives us = 26%.
Our kill options are better if you recovery properly Fair shouldn't even be a problem, we have Dash attack to Shuttle loop at high percents while Mario doesn't have reliable kill set ups. I would stay just outside of Mario's range and then punish what ever he throws out with a DA or Grab, if Mario approaches us we can beat his DA with Dtilt if time correctly or simply use M-Nado and get easy percentage.
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I'm not gonna do the 50:50 raito's people do with match ups because i don't know how that stuff works. If there's anything missing in my post or if anything is false please tell me since its my first time doing something like this.