The most obvious thing to me about this match was that you made very little use of your shield. You rolled a ton and spotdodged a little, but you didn't use your shield very well. You rush into things a lot, so my advice is to take things slower and
think about what you're doing. Try not to look at what your character is doing, but what at your opponent's character is doing. If you shielded more, you could have punished more.
You roll when there is no need for it. For example, at 2:00, you sent Falco off the stage and he is attempting to recover. As he's offstage, you roll back and forth a few times. There's really no need for it, and I don't want to come across as being ignorant here, but it's usually a sign of a reliance on rolling. Instead of rolling, perhaps you could have positioned yourself at the ledge in anticipation of his return to the stage, i.e, if he get-up attacked, you could have reacted by shielding and punishing. Or maybe you could have took it a step further by jumping off the stage and stage spiking his recovery with Bair. Fox and Falco's recovery is very gimpable; when you see them hovering in flames, not moving, jump down and spike or stage spike.
Work on improving your punish game. He used attacks with a lot of end lag, like his Fair, and you missed the punish.At around 3:06, instead of punishing his end-lag, you rolled away.
Again, work on using your shield more. You were over-aggressive, running into projectiles and aerials a lot.
At around 5:52, Samus fully charged her Charge Shot. When this happens, be aware that your opponent is going to want to get rid of it as soon as possible, especially since you were at kill percent. Getting killed by that Charge Shot is definitely an indicator that you were playing far too aggressive, and rushing in without thinking. In the future, remember to play much more defensively when your opponent, be it Samus/Lucario/Robin etc, has a fully charged projectile like that. Expect them to throw it out. They'll most likely use it when you're recovering back onto the stage, when you are up in their face, or when you're offstage and near the blastzone. This mistake ties into not using your shield.
At around 6:52, you used Dark Pit's multi-hit jab. Although it worked this time, I would not recommend using it often. Pit/Dark Pit's multi-hit jab is very risky as it pushes people back and out of it very quickly. However, their 1-2-3 jab is very good, and works as an excellent spacing tool. If you're used to using the multi-hit, I know it can be a tough habit to break. Just get used to holding down the A button instead of rapidly pressing it. The only time I would use the multi-hit would be when my opponent is recovering from the ledge. If you stand at the ledge and use the multi-hit, they will get caught in it if they try to get-up attack, jump up, or stand up from the ledge.
You throw out laggy moves often. You D-Smash a lot when your opponent is not near you. Dark Pit has excellent moves to close the gap between him and the opponent. Try using F-Tilt and D-Tilt, both have excellent range to poke at your opponent. I also think it would be advantageous if you learned how to short-hop. Maybe you know this already, but don't implement it in your games. Short-hop fairs are good for spacing out your opponent.
I don't think you use your aerials enough. At around 8:18, Mario was jumping all over the place, and you tried to hit him with grounded moves a lot. Dark Pit has fantastic aerials to make good use of. Next time your opponent keeps to the air like that, use your Fairs and Nairs to keep the pressure on.
Welp, I was bored, and that's what became of it. Hopefully you found my long-winded essay somewhat useful. Ask if you're not sure what I'm talking about in parts of that.