Lugi's utilt wrecks you. horrible horrible move.
Anyways... This is kind of a nightmare match if you go into as you do all your other matchups. You really have to play quite differently. I just have one word for Fox mains out there: Usmash.
Seriously, Usmash is a saving grace in this match. You can usually trade with or beat Luigi aerials with it... and end a lot of his shield pressuring game, since his range is bad enough to allow for shield Usmash's use. And since Luigi is slower and floaty, landing lasers to refill it is a great idea. His only fast approach is tornado, which is punishable, when expected.
You also really need to be spot on with your edgeguarding here. I actually think Fox wins the edgeguarding/recovery war here, since you can cover most of his options with one placement, where as, he has to guess you out to punish your recovery. Shine beats all of his stuff, but I wouldn't rely on it. rising dairs, nairs, and fairs can really screw his recovery over, and they're all much safer than shine. Then supposing you miss the rest, edgehogging his upB gives you a free smash on stage. not too shabby.
Bair spacing (as I've grown to use even more lately) is VERY nice in this match... as are situational fairs. I would probably stay away from any kind of JJC, although Uzi got JJCS>dash attack to work, so maybe...
If you guess luigi in the air, a FH dair is very good, but I would not use it if the luigi is grounded.
Luigi just has a LOT of options here... He's hard to guess out, and has very nice quick attacking moves, great priority, gets out of your combos easily, and combos you back. Pretty harsh... Fox needs to use his stronger attacks here, with better spcing, rather than trying for nuts combos.
Overall, Luigi wins the matchup. Good shield pressure, escapes from combos, air control, variety really help him here.
I think with good spacing, smart play (of course), and good edgeguarding, the match gets closer to even... but it's still quite hard. Lasers really help Fox here, so i could imagine camping for a lot of the match, and being quite effective with it.
For a score, I'd have to say anything on a range from 6-4 Luigi to 7-3 Luigi here... just a hard matchup, guys.