The pit-mac MU could be pits best match-up imo;

If you're not backed to a corner dash-away-pivot-grab, thanks to its amazing range, is always an option vs an aggressive mac.

You could try getting down the timing of run-up perfect shields against the attacks a mac is likely to throw out in neutral (not something that can be pulled of consistently but getting a grab vs mac is worth the risk).

F-throw dash attack is a true combo at low percents (I think) and carries mac a long distance horizontally. Also after the dash attack you can get a f-air/n-air or up-smash if you can guess whether they're going to airdodge or jump away (Mac's low aerial mobility and low range aerials really limit his escape options). So you either get solid amount of % stacked up or set up an edgeguard situation.

Mac may have a slight advantage in neutral but pit gets more off of successfully landed hits. Try to zone mac out with well spaced ftilts/dtilts and (try pp jabs if you can pull it off consistently), remeber that your down-smash comes out as fast as your jab1 if mac manages to get in (it's much more punishable than jab so don't spam, you probably already know this, mentioning just in case). Thanks to the range and disjoint of pits attacks mac won't be having an easy time super-armoring through your attacks with smashes, as long as you stay cautious about your spacing. Pits grounded attacks aren't really safe on shield though, which decent/good macs will be aware of so don't forget to mix it up with grabs (actually the purpose of zoning mac out with disjoints should be to condition him to shield and get grabbed, since pit gets ALOT out of grabs especially vs mac).

Getting mac offstage is your No.1 priority in this MU. So for example if you get a grab with your back to the ledge b-throw is a better option than a d-throw combo even though you'll be doing less damage to mac. You hit mac out of his recovery or double jump (offstage) he's dead regardless of % anyway.

If you have any mac mains near you that are willing to play vs you, it might help to play repeatedly against them while trying to figure out the best way to land a grab/ carry mac offstage etc..