My god, just finished it with my 11th character. Why the hell is Luigi so light?!
He's actually pretty middle-of-the-road. He's a touch lighter than the likes of Falcon, but that's still heavier than ZSS, Sheik, Marth, Rosalina, Pit, Ness, etc.. That aside, he's mostly the way he is because of his combo game, which is only much rivaled by Shiek. I mean, hell, he has chain throws.
Plural. Granted, they're character-dependent and all, but his auto-comboing downthrow along with one of the game's better projectiles and even some solid KO moves (F/Usmashes, Up B, Down B, Bthrow, Nair) on top of some nice gimping tools... and you've got a character who's very solid... at 1v1s. Luigi's far more difficult to get much done with against multiple foes, though, as you really can't get off throw combos, yet Luigi lacks the movespeed to really do the rushdown game without poking and prodding for openings with fireballs and whatnot.
Still, I've found myself racking up damage faster with Luigi than just about any other character, which is pretty nice on someone who has more KO moves than bouncing fish, Uair, and Usmash. The key I've found to using him is to use his tilts as infrequently as possible unless it's part of a string-- that's all they're particularly good at. Boxing shields with jabs to sneak in a grab seems like it'll always be his best melee option, while everything else boils down to aerials, fireballs, and cyclones, with the occasional smash on a read or such. I imagine using a lot of cyclones and focusing in on his air game might help with all star, but I've really not had much luck in free for all formats with Luigi, heavily as he relies upon that downthrow game... Shield boxing is particularly iffy against AIs, though, so I'm not sure how much help any of that might be.
I recently completed the DHD challenge (as a result, I'm actually pretty decent at DHD now... which is pretty funny), as well as Falcon's 'normal without healing', and the latter was one of the easiest I've done yet-- Falcon's so
solid in this game. That, and AIs don't seem to understand his Fsmash, so you can just elbow all day on flatter stages, while his BnB Uair strings make the CPU's laughably bad platform management all the easier to take advantage of.
In fact, that just occurred to me to mention:
at every level, AIs are extremely susceptable to camping their platform fall-throughs. As DHD, I got plenty of free KOs just camping under the platform of an elsewise potentially problematic stage like Mario Kart or the like, while it had me clearing the likes of Battlefield-style stages without damage at all once or twice. Usmash, tilt, and air all worked wonderfully for both damage and KOs quite safely. Definitely recommend that everyone struggling make it their first priority to abuse platforms whenever possible... or at least their second or third, given how important the whole 'safe damage' and 'easy KO' bits are on the flatter areas.
I think we might be able to reduce characters to their best All Star tools, actually... As an example:
DHD
-Damage: Side B, Fsmash, Usmash
-KO: Fsmash, Usmash, Uair, Neutral B, Nair
-Platform Camp: Usmash, Uair, (Neutral B unsafe)
Maybe listing out their tools in order of usefulness? DHD's side B is, on its own, nearly enough to get all the damage you'll ever need, while Fsmash will handle most of your KOs and Usmash works for most of the platform punishing you'll be doing. Not any perfect example, of course, just what worked for me-- making up a little guide like that might prove helpful to people, nonetheless, though.