Thanks for your reply.
What is FH? I understand that SH goes for Short Hop but FH?
What do you mean by that: "the c stick will either cancel or override the control stick"
I think that i will practice more with the c-stick because i can't execute some specific moves simultaneously, like moving back + Bair. Just like what you said...
Sorry for the super late reply, I've been busy. FH was answered, I'll just add some specifics. When you press jump, your character enters something called "jump squat." It's the animation where they kinda bend down a bit to get the strength to launch themselves upward. IIRC, Luigi has 5 frames of jump squat (maybe 4), so it takes him 5 frames to leave the ground. If you're holding jump when jump squat ends, you'll do a full hop (the taller one), but if you hold for 5 frames or less then you'll short hop.
Let's say I'm playing as Luigi. Luigi is airborne facing right with no momentum. If I hold left on the control stick (grey one) and right on the c-stick, Luigi will execute a fair but he won't go anywhere horizontally, he'll just fall. As soon as I release the c stick, he'll start moving left. This is because the c stick is still inputting a direction, even though it only input A for 1 frame. In every other smash game, the c stick inputs A for one frame and a direction for 1 frame, but in smash 4 the c stick inputs the direction until you release it (that's why you can charge smash attacks with the c stick). Changing your c stick to "Attack" in the controls menu reverts its behavior to previous games, but you can't use it to smash attack anymore.
I made myself use the c stick for every aerial for a month or so just to learn how. It definitely helped my game.
How do you guys practice? I feel like I've sorta "mastered" Luigi. I'm aware of all his options and movement. I can jumpless cyclone very well. I feel like I know everything about the character. But I am still not a top player even in my region. Any thing I could be working on to get me to that next level?
You probably have, tech skill in this game is trivial. When RARing is one of the hardest techs, you know the game's easy (from a technical standpoint).
Knowledge is very important, you need to know exactly what beats what in every situation.
Otherwise, work on your mind games. Watch Ally and analyze his play (it takes me ~15 mins to fully go through a ~4 minute game). He's the king of mind games imo, smartest player in smash.
When you practice (i.e. every thing but tournament matches) go for weird stuff. Stuff you don't think should work, like d-throw -> downsmash on fox (I've hit both hits of d smash with that string before). Try the jankiest **** you can think of, and eventually you'll find some super situational stuff.