Right from the beginning of the dubs match, you could've Baired Game and Watch off stage and edge guarded him. The big points to take from this is to abuse the speed of your aerials and use remember that most characters can be edge guarded using well spaced and timed Bairs, Dairs, and Fireballs.
You should make it muscle memory to instantly waveland on stage by tilting away, hold for just long enough after release to jump and make the input a backflip, then wave land on stage. This lets you stay in the action, abuse invincibility frames, and let you survive much better past 100%.
In dubs specifically, a great way to work with your teammate is to do SH Dair an opponent. Naturally they'll shield and attempt to grab you OoS. Let your partner know if he sees you doing this attack, be prepared to go in and punish the opponent while they're grabbing you.
If an opponent is above you, standing or laying on a platform, an ideal attack is to jump (full hop), instantly do Uair, fast fall, Nair and L-Cancel. It keeps shielded opponents in shield stun (which you can either finish with a Dtilt if it's about to break or grab if not) and non-shielders in a nasty combo starter. I noticed you had a good opportunity to do this during the first dubs match.
Avoid rolling. Any higher level opponent can react to your roll and punish you...and in a lot of cases, put you off stage where you'll most likely die. If you're close quarters with shield up, WD OoS backwards, do a Nair SHFFL OoS, Grab OoS, or USmash OoS (especially if the opponent is right behind you to get caught in the beginning of the hitbox). If you REALLY want to dodge, spot dodge is ok. Notice how in match two for dubs you got punished with Mario's FSmash for your first stock. Also, remember you have super armor if the grab hitbox land on the opponent's hurtbox at the same time as the opponent's hitbox.
Careful about throwing out that Misfire, if any hitboxes get in your way, your attack won't hit. This is especially the case for projectile wall characters like Link and Mario. Try to reserve it for combo finishers or reads you're pretty sure you'll guess correct.
For the sake of dubs, a rather "safe" way to throw is to do BThrow since the swung opponent acts as a hitbox and can sorta guard you on ground. Plus it's great way to do what Luigi does really well in dubs: get one opponent off stage so you can double team on the other opponent.
Never ever ever ever accidentally press Dash Attack. That mistake can cost you a stock in a lot of cases. The only time it's ever safe to dash attack is if the opponent is shielding right next to the ledge so you can push them off...and even that has a few matchups that end up countering you during the end lag.
Although you can't really edgeguard Diddy, in general, the two ways to hit vertically edge approaching opponents while staying on stage are SHFFL Dair at the edge or a really well spaced Filt with a downward angle.
As for general things, at least from my personal opinion:
Try to avoid jumping. If you're facing a high level opponent, you'll find that Luigi is a sitting duck in the air if his opponent isn't stuck in stun lock when dealing with neutral game on stage. In other words, your go-to neutral game moves should be the ground based ones.
Movement is looking pretty groovy, however that doesn't mean you've conquered the Luigi footsies. The fastest means of getting from one side to the other is alternating between WDs and Dashes in the same direction. It takes a lot of work, but man is it worth it. Also, your lack of movement (remember, this is all coming from the perspective of someone who's trying to make Luigi a super fast rushdown character) doesn't really put much in the way of pressure on the opponent. When faced with high pressure players, you'll find this leads you to getting "trapped", or easily susceptible to being put in bad positions for neutral game since the opponent is positioning around a stationary player. This especially is a problem for characters like Marth, Roy, Ike, and Sheik (I can tell you from a lot of personal experience that those grabs are the bane of Luigi's existence). I'd recommend not letting the opponent get the upperhand by using dash dancing more often when you're not applying pressure. Like Boomer3d said, spacing is really important because it's how Luigi "get's in" and starts racking up the combo damage. As such, a high level opponent will know that and try to make sure you don't have the proper spacing.
Your punish game can become better, though it's looking pretty good so far. This is honestly a thing that just gets better with time and experience. Don't stress about it, just try to push those combos farther over time.
Other than that dude, you're doing amazing, seriously. Keep it up!
hold til jump to execute backflip then waveland for max distance and least time. In neutral I work off a set of approaches working from dash dance unless they're at a disadvantage (off stage or teching), in which case I play rush down tech chase covering options via fireballs, Dairs (perfectly spaced spikes for attack getup or standup), DSmash, Grab->DThrow->Chaingrab tech chase, DSpecial, or Shoruken.
