oh boy i didn't miss the discussion this time! anyway, as usual, ill split it up into the 3 phases for each character, and give an analysis for both followed by a synopsis.
NEUTRAL
k, lets get this out of the way. Mario can't approach for crap against mac. his only 2 solid approaches are a empty hop or an aerial. he COULD run up dash attack or shield, but those are both punishable by an ftilt or super armor smash attack. so how does mac punish an aerial? usmash. how does he punish an empty hop? usmash. if its an aerial, he super armors it, if not, you get a free smash attack. mario has to get really creative in his approach game, and gets outspaced by mac easily if you are using p pivots and dash dancing of course. mac can straight up walk up to mario, and start pressuring him with jab, dtilt, ftilt, p pivot ftilt and utilt, and DownFsmash if you are looking for shield breaks. Mac doesn't care if mario is throwing out dairs or bairs or nairs, and mixing it up with a single or double jump aerial or empty hop. Little mac has one answer: usmash. yes you could wiff it, but only if you are rash and impatient. even if you do wiff, Mario may not have enough time to get in for a punish. the only real danger is a dash or shield grab, but that's only if mac is misspacing, or throwing out unsafe moves. Mac being played smart typically walks over mario in Neutral.
FOLLOW-UP
Mario's follow ups are ridiculous. a single grab can net him 50+ percent if done right from 0. it can lead to kills, gimps, and almost always gives him stage control. no need to list his strings and combos, we all know it. In short, if Mario finds a way to win neutral, he will almost always get a follow-up. While mac has a large scale advantage in neutral, he also has to win it multiple times before netting a stock, since his followups on mario are subpar. and since mario is a midweight, only a few combos and strings are helpful to Mac. dtilt follow ups are what you are looking for, and they can string into different things at different percents. Low percents are dtilt>ftilt or dtilt>side b. mid percent is dtilt>p pivot u tilt>usmash or up b. high percent is your dtilt>fair strings, or a dtilt>smash attack if you are baiting out a air dodge. kill percent is your dtilt>jc up b, this combo is true if done right. besides that, there isn't a lot of other strings for little mac on mario. the good news is that macs main combo tool, spacing tool, and safest move are all packaged into dtilt, and will win him neutral the most often. just make sure to follow up, as mario will punish you if you aren't playing right, and potentially kill you after one grab.
EDGEGAURDING
lets give a list of moves each character has to edgeguard the other with:
Mac:
Dsmash
Fair
Dair>footstool
Nair>footstool
Bair
ledge trump
Run off side B
Mario:
Fair
Dair
Nair
Bair
F.L.U.D.D.
Cape
Ledge trump
TBH, i might be missing some for both, but these are the moves most commonly used for both parties. Mario can edgeguard more effectively than Mac can, but mac has multiple options too as well. for Mario, his job his easy, predict a low or high recovery, and punish accordingly, in all honesty, he really doesn't even have to mix up his tools when he edgeguards, as it all does the same thing to mac. Mac can punish a low recovery up b with a run off side b or ledgetrump, to either grab the ledge or hit mario. fair is for a mario recovering high, bair for a mario recovering under the stage, run off nair or dair to footstool if you see him recovering low, and you are looking to net a stock. (pet peeve of mine, little mac has more than one way to edge guard, and shouldn't be afraid to run off stage to get a kill, i want to kill this misconception about him.) Mario still holds an advantage in this phase of the game though by far, as he has a 50-50 chance of predicting macs recovery, while mac has to read marios recovery, and see if he recovers low for a ledge grab, recovers low but goes over the ledge, recovers high, or uses cape to stall before using his up b or just jumping.
Overview:
Mac has all the tools to win, but can't afford mistakes, or he will get punished by Mario severely. i would compare this to the Captain falcon/Marth matchup in the fact that mac wins if the player plays almost perfect and slowly chips away, but mario needs mistake or unique mixup to get in and net a stock. i would give this a 60/40 mario's favor, since mac has to work harder than mario does to win here.