Game and Watch
I joke a lot with my friends that all of Lucas' match ups are "run away and spam PK Fire." When asked what to do against GW, I say "run away and pray, a lot."
In response to what CJ said, we had a Lucas player at Final Smash 5 who went 1-1 with Hylian's GW in pools. Hylian also had to play him (Pierre) for a tiebreaker to get out of pools. Hylian 2-0'd him, but both games were really close. I also play UTD Zac on a regular basis, and he is a NASTY GW.
I find that I can sometimes punish the Dair with a spaced fsmash, and despite everyone else saying it's a bad idea, players get predictable w/ that key and you can Usmash that if you see it coming for a glorious low % kill. I shield grab the turtle if it's not spaced and just run away if it is. I usually roll behind the GW if they get turtle-happy. I don't even bother trying to gimp him. It's near useless. I use PKF sparingly. It's a good mixup, especially if they think "hey, they won't throw a PKF because I can bucket it."
Marth
I play against DallasPhat a lot and he's one of the best Marth's in Texas.
I also encourage him to release grab me in friendlies. Oh, and thanks Tyr for mentioning that EIDI does nothing for Lucas. I've been saying that EVER SINCE I found out about it. It will not help you here. If you are striking stages, try to get on Final, Smash, or PS1 (if that's neutral). Strike Battlefield and Yoshi's also (too small). Run away and spam PK Fire while he's onstage. If you can send him off the level with a back throw you can use PKT to rack up damage and gimp/stage spike him. Learn zap jump. You will be edgeguarded to death (literally) if you don't. If your timing and spacing is good, I think you can run under marth when he does a FH Fair.
Donkey Kong
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I play against DK's every now and then. I just use PKF a lot and nair him to death if I can get inside his range. I think this matchup is exaggerated. It's not harder than Marth. I don't play any super good DK's though, so I may be wrong.
Meta Knight
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I've played against Dojo in one friendly in which I go 0 to 70 on him and then he 3 stocks me. I also play w/ Infinity from time to time. It is a total nightmare. Screwing up the zap jump is like a free lost stock. I find defending myself w/ PKF very hard to do, given that he's SO quick.
I'll try to get some vids up of me playing against UTD Zac's GW and Dphat's Marth. IDK when I'll be playing Infinity again.
I know i reiterated a lot of things, but hopefully my viewpoint is useful.
And seriously, I'll get vids up soon: I get to play the deadly 4 all the time.
EDIT: @Oats: I may be going super noob here, but what exactly allowed you to wreck MKs
on Luigi's Mansion? Was it lagging stuff on the pillars or what?