Neutral

For neutral, I think at a distance Luigi has the ground game advantage with how strong his dsmash is and how upsmash is safe on shield. Marth can attempt to stuff it out but often it clanks and gets easily whiff punished. Can't really whiff punish unless they're at opposite ends of DL. Being grounded vs Luigi is only good if you can stuff out his WD when he’s cornered.

I believe Marth should primarily be in the air to easily dodge those attacks.

Luigi FH at you is a horrible idea for him and very imprecise since his drift is bad.

Luigi’s SH shouldn’t threaten your sword disjoint unless he’s trying to catch your landing, which you just need to mixup accordingly. SH fair or dtilt in place beats that. So that’s the primary mixup I play.

I prefer being in the air vs Luigi since his main threat, dsmash, is pretty committal so I have time to punish. SH then mixing that up with DJ or fair is pretty good vs dsmash in.

I default to jumping in place if the Luigi is doing braindead approaches then I take space with SH in or even walk if they’re waiting more.

Use aerials and empty hops to mixup their approaches and zone them out.

Move in slowly with empty approaches or if they are overzealous, grab / dtilt them.