Man, why the hell can't I play against cloud? It's the same feeling I got playing against Shulk when the game first came out, until I figured out how ridiculously punishable most of his attacks were. Cloud on the other hand has very minimal endlag on most of his attacks. And playing as Lucas, I have fucking terrible roll-punish options, so Clouds just roll around the stage charging limit breaker and covering half the screen with that fucking buster sword and I can't even get close. Got 2 stocked by an obviously terrible cloud a little while ago. Ugh.
It can seem difficult at first, but it will probably just take practice figuring out how to beat them. There's a few key points that will help:
1. His side smash is strong, but has a long animation, and somewhat long ending lag. If he whiffs the side Smash, you have a good amount of time to hit him from the other side.
2. If he tries to go for the Down+B (tornado) on his limit break, whiffing that gives him a very long ending lag, so that one is very easy to punish.
3. Without Limit Break charged, his recovery is straight up garbage. It's so bad, Ganondorf almost laughs at him. If his meter is low and you can launch a decent distance, even if it's not a direct KO, he probably can't recover.
4. If he starts up his Cross Slash (side B) on you, shield it. Even if you don't manage to block the first two hits, you can still block the third series of hits.
5. I don't play much Lucas myself, so I'm not too familiar with the matchup, but I would think PK Fire is pretty good at punishing the rolls. Also if he whiffs anything big, that up Smash is great. If he's spamming his neutral B at you, just PSI Magnet it up. I think you can do it to the Limit Break version, but I'm not 100% sure on that.