I'm going to try to be very specific in this critique of these two videos because I'd like to make some points about how Lucas is commonly being played right now by a lot of people.
First of all you have a good overall playstyle. You don't rush in unnecesarily and you have pretty good spacing. You take advantage of your opponent's mistakes effectively and it's obvious that you are thinking while you're playing. The one thing I would change about your overall playstyle is to play a little bit more defensively. PK Fire can work wonders for you if you use it a bit more. Obviously be intelligent about it and use it as a spacing technique. Oh and don't roll so much. Some of your rolling was just completely pointless and could have lead to some serious punishment.
The first question anyone needs to ask when watching a video of themselves is: what mistakes did I make that lead to punishment?
Fair
Fair is a very risky aerial to use. It has a small hitbox and leaves Lucas very unprotected. If you watch the first video especially, I think every single Fair you attempted on a grounded Marth was either shielded or hit by one of his attacks. However, when you hit him in the air with it, it was succesful. You had a little more luck with it in the second video because you used it while Marth was in some lag from another move or by switching up the timing on your short hop slightly. The problems with using Fair on a grounded opponent is that you have to fastfall to hit with it usually and this leaves you with lag which leads to punishment. It doesn't take much lag to get punished in Brawl. You want to try to avoid using Fair as an approach unless your opponent has made an obvious mistake in spacing or lag time. Sometime full hopped dairs can work better as approaches. I often use autocancelled Bairs on characters like Marth because of its reach. Short hopped Nairs are a little harder on Marth because of his range but is a great approach on a lot of characters.
Falling Dairs
Avoiding being juggled by using falling dairs on opponents can really hurt you. There is tons of lag at the end of dair if you land before it's over. This hurt you several times. A lot of people are doing this and really hurting themselves with it. If you're going to do a falling Dair to avoid juggling make sure that you're going to land on the stage after the move has completed. Some better choices in some situations can be Bairs and occasionally even PKT1 or PKT2. If you use PKT2 shoot yourself straight down so that you floorblast. Be very careful with PKT when falling because if your opponent predicts it you'll get badly punished.
PK Thunder
Misaimed PKT2 cost you a lot especially in the second match. It can be a very predictable move. While recovering with PKT2 it's almost always better to aim for the ledge rather than try to make it onto the stage. Many times you took Marth's Fair in the face because you took this risk. One time you lag cancelled the PKT2 and avoided punishment. I don't know if it was intentional but it worked out very well for you so if you're going to try for getting on the stage that way, go for the lag cancel.
I also noticed one of your edgeguards against Marth was poorly executed in the second video. Marth was approaching the stage and you sent PKT1 straight down into him which knocked him back up. PKT1 is incapable of sending opponents downward, so by sending it through him in a downward direction, the back of the head forced him upward and back onto the stage. What you should have done is gone around and hit him with the side of the head into the stage for a stage spike. This could have been an easy kill for you. Keep it in mind.
Overall I really liked your playstyle. You don't rush in carelessly like a lot of people do. Your Marth friend counters waaaay too often and it's giving you a lot of free openings. This won't always be the case and you'll have to play more defensively in a lot of games. But mostly just keep up what you're doing and think about the things I mentioned.
