Vs NAKAT, you need to camp the ledge with trampoline. You were trying to go toe to toe with Fox's neutral, but it's not going to work. Take your time and think out your setups more. You have no reason to go over there to him without some setup planned / going. I couldn't tell what you were going for half of the time.
If he's letting you charge, get Keys or galaxian in your hand. A galaxian OOS at 0% can lead to 42%. At mid %'s, it leads to 30% combos.
https://www.youtube.com/watch?v=n_1NnfFjajE&index=33&list=PLc2mEAQQLG6gYX1BfkA_cc9hgLuKZg_Vv - me vs Fox from last Sunday. This is the second time I've played Jsalt in tournament. Looking back, IDK wtf I was doing. I'm ashamed to say that was me. I can say for sure that I wasn't focusing on him enough. Pac-Man has an entire moveset besides his fruits, and I wasn't using it enough.
Vs OCS James, use trampoline instead of hydrant for control. Hydrant isn't bad, but against a character as slow as Luigi, you can get away scott free every time unless he gets a lucky misfire. Stand behind trampoline and pellet shield the fireballs (let the pellet sit on the ground). Charge to a Key or galaxian and go from there. Pester his jump in with Fair, Bair, Utilt, and pester his landings with Dtilt or Fsmash.
I don't Vex had a firm grasp on Sonic. I think the MU calls for camping the ledge, but maybe that's just me.
I'll watch the other one + go into detail later.
Edit:
https://www.youtube.com/watch?v=4F5tskxuprM&index=32&list=PLc2mEAQQLG6gYX1BfkA_cc9hgLuKZg_Vv
I have no idea what to do in this MU. I may try to fight Peach like how I fight Luigi, AKA camp the ledge because her combos and crap do so much %.