Ok so assuming you are put onto a scenario where you are faced with going to FD or choose to opt to fight him head on (obviously running away back to platforms to safety as mentioned previously is safe, Also prolly think of a game plan to deal with him while you camping on their haha) retreating fairs and bairs are okay against mac tho theyre risky when u have to land back to the ground. Empty short hops are good to bait out stuff (baiting out is wonderful in general for this matchup), key things to keep in mind really is to take control of center stage and force him off the edge(being on the edge for you gives him way more options to go for you so its not always the best idea some little mac's actually want you to do that). Its always good to space yourself away from him maybe two fsmashes(or 1 fsmash for the most part) apart if you can and then camp with pikmin throw, when approaches you his safest option to come at you is a dash attack, which we can just fsmash or sheild grab for a free punish (same with his jolt hay maker although if ur on the edge chances are he won't use it for fear of sd'ing but good little mac's will use the haymakers anyways and then do some silly thing were they can snap unto the ledge) Also keep a purple on you because throwing purples from a reasonable distance removes his KO punch,whilst regular dmg from pikmin latch doesnt really remove it at all. Shield is super safe in this matchup because fortunately,his grab isn't the best out there, using OOS jab to grab or fsmash is nice, however if u stay in ur shield too long know that he can do alot of shield dmg so don't rely on that too often. Bait out his counters and air dodges, especially when he's trying to recover because if you read that its a free gimp, or on stage free dmg this is one of the time where we actutally chase someone in the air cuz his air game is so bad and unlike most matchups for oli its worse than ours lol.
As we all know if you are trying to get back to stage besides using platforms to get back, he can do that also so just be aware of that and you could probably punish him from there too, don't ever land back on stage unless u really need to because landing vs mac on the stage like we all know can be quite frustrating. Having a white pikmin is wonderful for this matchup as pivot grabbing beats his super armor(grabbing in general really but normal grabs are unsafe) and you can combo from a grab so that's always helpful to know,Having yellow pikmin for the tiny extra reach for the fsmash is nice to keep him away seeing as from max distance (a fsmash away length from him) an fsmash hitting his counter won't have him actually hit you back for the dmg as it doesnt go that far on the ground. Oh and he can downsmash on the ledge to catch u coming back to the stage so be smart when u recover that way. **One more thing to know is that always having at least one pikmin on the front of him if he hasn't already killed it and uses counter the counter is forced to activate so you can possibly have a variety of punishes from this situation.
About platforms his just be wary for stages like battlefield with the lower platforms he can upsmash through them and he does have aerials (although they're terrible but can still prop you off and get u in a bad position if you aren't careful) Also, while being on platforms be wary that his up B is in fact a useful kill move so don't thnk your always home free on them. Like what was said before me, just try to ban fd,although good lil mac's will already know that it would be banned so they practice on platform stages, I've read around on the little mac boards and it seems that they like to pick lylat since again the two outer platforms he can upsmash through, castle siege (he gets saved alot by the stage transitions although you could easily camp him on the higher platforms, especially if you break the statues he cant get on the on the 2nd transition without being very risk,the 3rd transition(lava fd one) is really good for him but it doesnt last that long compared to the other two, the first one is really bad for him since he cant even reach the platforms so he will likely not approach and wait till the stage transitions, Delfino perhaps is a good stage for and against him although its admittedly easier to camp here on certain parts so you just gotta be mindful at that point. He will most likely ban smashville, or duck hunt( duck hunt you can camp on the top of the tree its hilarious watching him try to chase u if u do it, although do be mindful when the dog pops up he can jump on top of it and get on the tree and get to you may be unsafe as hell for him but its something he might do thats nice to be aware of, , he can also kill you at 20% if he gets the entire Up B to hit at the top tree so be smart here if hes up there with u somehow). Halberd little mac's will also counterpick besides castle siege because its a little bit easier for him to chase you on the platform, dont ever stay on the edges of the platform though because the slopes where he can stand on he can still upsmash you, and ofc if they stage chooses to hit you instead of him he'd like that alot. Oh and one more thing when the stage transforms and goes on the ship its wonderful for him because the entire platform transforms so that his upsmash can hit through it, so again be aware of that and prolly would be safe to camp on platform once the stage transitions off the ship. They probably might also like town and city as well because some portions of the transition don't have platforms so you will definetly forced to fight him head on.
Play this matchup patiently and calm but precise, don't lose your cool and always remember even if your at a stock deficit and he has a KO punch, its just a little gimp away from evening the score back and winning, don't let him break your spirit just be careful and don't roll alot or he will dsmash for days, but most of you already know that. But yeah thats just my two cents to go into this a little detailed, I am prolly missing stuff, but thats what comes up to mind for me atm when I play against him.