EDIT: Yes, it's at the ****ing top, because i feel stupid.
When I wrote this, which was during 5th period, I had in my mind some sort of warped version of Marth that was half-way brawl and half-way melee. Marth's range is not that crazy. This match up is not as hard as i portray it. Heavy editing coming later.
.kR0, i'll play you as a marth. My marth was tournament level in Melee, I'm not sure how good it is in Brawl (range nerf huuuuuuuuuuuurts), but maybe you'll get some ideas. My brawl code is listed to the left, what is yours?
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The problem with fighting Marth as a Lucas is that every single attack he has outranges nearly every single attack that you have. His fair destroys all of your aerials, barring your uair, which is fairly limited to targets above you anyway. Your main focus should be to pop him up into the air above you, and uair/utilt him. Eventually he will be able to get a dair out, but if you can see it coming, you can spotdodge it and get away with another utilt > uair.
What can you do to pop him up into the air? Unfortunately, your dash attack has been severely nerfed (from Ness's in melee), as it has had nearly all of its range removed. It would be perfect if it had more range, but unfortunately the slight start up lag is crying out for a fsmash from Marth. The utilt would knock them directly into the air perfectly, but you have to be incredibly close to Marth, and, if the Marth is any good, they will be spacing to keep the tip of their sword at you. It'll be hard to get inside. A PK Fire would work well for getting him into the air, but, while the lag time on it has been severely reduced to the point where it is a viable spammable projectile, it still isn't fast enough for use in combos. Coming from above with a dair would be fine if you weren't facing Marth. One cannot simply dair into Marth, it is folly. His utilt will **** you. His usmash will **** you. You simply cannot get through him.
Use any of your smashes, and you are begging to be fsmashed. His fsmash simply outranges, outprioritizes, and most importantly, outruns all of your smashes. Your usmash is simply much too slow. You might be able to get it off ONCE in a single match, against an opponent who has never played a Lucas before, but aside from that, your opponent is not going to approach you from high enough in the air to hit him with an usmash. Your dsmash has some utility against dodgespammers, as it stays out long enough to hit a spot dodge, and also hits behind you so it will own a roll dodger. However, it's hard to get this to work, and if it misses, you get punished with a fsmash, again. Your fsmash doesn't have nearly enough range to be useful when going up against Marth; you will need to combo him into it in order to get a hit, and this is DIFFICULT to do against Marth.
I foresee, until the metagame for Lucas becomes more developed, Lucas v. Marth matches will end up being rolldodge fests until either Lucas gets a dsmash off or either player gets a grab off. This is NOT good for us, because our throws suck, while Marth's don't. So what are our options? Use one of four ineffective ways of getting him above us where we can destroy him with utilts and uairs and fairs, or play a rolldodge game with him, getting owned by his grab unless through some kind of miracle we can get a d/usmash on him. We have no options.
However, we can keep him at bay with sh'd PK fires. These are only good for so long, though, as they are easily avoided. They aren't good for that much damage, but simply keeping him away from us. Maybe, if we're lucky, he'll jump over one, and if we're even more lucky, we'll have enough time to slap him with an uair. More than likely, though, he'll be able to get a dair out before that happens. If we expect that, we can fake an uair but instead fastfall to an usmash. However, that'll only work until he catches on, which, if he's any good, will be after the first time he does this. We are forced on the defensive.
Which, luckily, we are extremely good at. Backward short hopped bairs DIing away from him, SH'd PK Fires DIing away, and if they're far enough away, we can angle a PKT to blast them away from us. He can't approach us with sh'd fairs if he can't get past our wall of PKTs. (We should name that something. If Jigglypuff can have a Wall of Pain, we should have a Wall of Fire or something. Is anyone particularly against naming this the WoF?)
However, with no decent offense, and our only damage coming from PKFs and the occasional grab occurring in the dance of the roll dodges, Marth ***** us, in the a**, hard. After all, real kings wear tiaras.
We do have the advantage edgeguarding, for now, though. Shooting PKTs at an angle into Marth if he's high up, dairing him to interrupt his bup, bair spiking him when possible. We're fairly ruthless in the edgeguard game.
tl;dr: Marth is a Lucas counter at this level of the metagame.