Lucas is a character that does very well making you uncomfortable. He rushes in hard and well and can be hard to deal with due to his great inherent momentum (of pressure, not literal momentum). But a lot of Lucas players suffer from relying too much on certain tools of theirs.
For instance, their side b is amazing and opens you up a crap ton, but a lot of Lucas players default to it in the neutral and don't have much else to do, as they're too used to using it as a crutch. If you can avoid side b, by caping, spot dodging, jumping over it, players who rely on it too heavily will crumble.
Another thing is that their pressure is incredible. Really really top notch.
But a lot of Lucas players rely on always being in control because of that great pressure. If you can get a grasp on your opponents habits when pressuring, and then break through and turn it around, they'll often have a ton of trouble getting out of a tilt mindset and making poor decisions as you pressure them.
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Now isolated from the matchup, I'd like to get something out there that will greatly benefit
ALL Mario mains,
and mains in general, and that's the effective mixing up of options and usage of tools. A lot of characters have metagames that advance at a snails pace due to having crutches. Easy and perfect examples are Lucas' easy button Uthrow kills, and Side B in neutral, Game and Watch's Bacon, and (surprise surprise) Mario's fireballs and, to a lesser extent, Dair.
A lot of Mario mains don't expand their ability to deal with diverse situations and adapt to their opponents adaption because they spend too much time leaning on fireball, and using it as a cure all. It is good. Really freaking good. And if you use it to great effect in the Lucas matchup, well that's fantastic. Unfortunately, that provides the opponent with an opportunity to do to you what I explained up above, which is to recognize your reliance on fireball (or any one thing, really) and punish that part of your game super hard. Because, until now, it was your all applicable solution you're now on crazy tilt and find yourself getting beat up for having a less developed overall game.
The solution to this is simple as it is useful. Practice without that tool. When you're playing friendlies with Mario, or any character, recognize what you use in great excess and stop using that at all. I can promise you that you'll find a great many gaps in your game when you're not using fireball. Patching this up is good, and it's what leads to making you an overall better player. Casting away your support and striking out with all of your tools creatively is what gives players that spark of inspiration that leads to crazy combos, insane reads, and dominating performance.
In case I haven't captured this well I'll quote who I learned this from so their can be more than one articulation to avoid confusion:
3) Character specific stuff. Try playing without your 'core' moves. For Doc, maybe eliminate Pills and D-Air from your game. With G&W, whatever you might be favoring with him (Hammer or Bacon or whatever)
Work out the dynamics and nuances of the game.
It's a big reason why every mainstream meta-game is slow as molasses and the popular players generally take ages to get anywhere. If Lucas didn't have an U-Throw that could be combo'd into or fished for at any % on any character, the 'better players' of the character would be a lot better, as they'd have worked out a lot more dynamics and depth of the character, even likely noticing that if Lucas didn't have U-Throw, he wouldn't be much different, given he can kill earlier and better in various other ways, but they're less obvious/simple without distinct insight and fluency with them, let alone in plain-sight the way almost everyone views everything.
YOU GOT THIS!