I'll give what I liked and didn't like rather than this is what you should do, since nobody is really a Lucas expert let alone me. So here it goes.
Things I didn't like:
mid/high % dash attacks, it didn't seem like they were leading into anything too useful. Lucas doesn't have too many great follow ups really high in the air. He can't get up there fast like Falco can. So on Ness atleast, I wouldn't use that too often later on.
Something that stood out to me was when Ness would to an on stage PKT2, and you shielded or distanced yourself from him. I understand that the safest option is to not get hit and wait for it to end, but I feel like that it's got to be punnishable. I know that as soon as it ends if he's on the ground he can act, but there must be a way to catch it. In friendlies I would probably try to catch it with a well timed down-b. Based on the knowledge that I can catch Warios side-B with it among other dash attachs. But in tournament I would have probably done what you did and waited. I notice you caught it like the last time he did it with a grab, thats great.
Things I'm not sure on:
Charging OU at the start of every stock. It gives you a nice finisher- if it connects. But the trade off is that you dont have those free seconds of pressure where you vie for a stronger position of the stage middle > side. It seems like an okay option when you're on a stage without a top platform to start on, like FD or Smashville. But when you do it on battlefield or dreamland not only do you use up your invincibility, you also end up getting punished by his PKF. Often leading into further punishment. Seems like this is probably only an issue in this MU though, since Ness has PKF to hold you in as you lose your invincible frames.
Up-Throw at high %s >115, personally I start looking for this too when I've hit them too much and its getting late into the stock I'll also look to finish with an up-throw. But I worry that it's people can DI it (correct me if I'm wrong) to be survivable for much longer than just 115%+ on the majority of the cast. So personally I'm trying not to get too attached to it as a reliable finisher.
This might not be something you can help, but those chain throws were a nuisance to you. I'm not sure 100% but maybe you could try to DI up towards a side platform on battlefield, otherwise you can try make your way to the edge.
Things I like:
PKF. You were doing some nice things with your placement and follow up to the PKF. You got some good grabs off of it. When I connect with PKF I like nair alot, it leaves you with alot of options for follow up. But grabbing is great too.
Down tilt. You were kind of on the right track using the down tilt (at least that's how it seemed to me). Watching this, I went ahead and tried putting it into my game. It's definitely nice at higher %s like 80+ when it starts knocking them up and you were doing some work with it, like dtilt to up smash a couple times at around 110% (that was hot). But then there were times when you were barely popping him up and then going for an F-Smash missing then repeating and he kept teching in place. A slower smash Up/Down to give enough time for the tech, or a grab (to catch a shield), or a combo starter like dair, uair, or down b could have been a good replacement to get more % on him.
Forward Smash. You got some nice connection with the stick. I like that you angle it up, presumably for the extra damage. Not much to say here, other than that.
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So that's All I've got for you, hopefully it will have some use to you.