I'm talking about the DK match, because I have the most experience with DK out of all the other characters you've thought.
First off, you're passed the phase of putting together strings of attacks to rack up damage, that's good. Don't get drunk off of this fact and run in headfirst against a DK. Although your opponent under utilized a lot of DK's moves, you know full well that his f-tilt is his most effective tool against you on the ground.
You can't fireball set up DK most of the time because of the F-tilt; use fireball too far and you can't capitalize, use fireball too close and you get a backhand to the face. Aerial Approaches/Ground approaches don't fair much better because you can get easily shield grabbed. The best way to approach a DK from experience however, is through the air.
Weigh the risk/reward of an aerial approach. On one side, DK's quickest and most effective move is the RAR SH Bair. He has impressive grab range, and of course powerful tilts. Luigi has quick ending aerials however. Let's look at a scenario:
Luigi SH Fairs a standing DK. The Fair is his quickest aerial, and has a good hitbox for frontal assaults (in terms of landing a hit). If you just go towards him with an Fair, he'll just shield grab you. Assuming you know this fact, you'll maybe try to space the Fair further away from him, just out of grab range. He still has uptilted F-Tilts and Bairs. So you space further back still, leaving him only with RAR Bairs. The DK will catch on to these SH Fairs and try to punish your repetitiveness with his most viable aerial. Here you can punish.
This goes without saying then, that you have to force the DK into the air if you hope to get inside. A standing DK (neutral position) who can do any move in his arsenal is dangerous and hard to approach. Catch him in the air? Well in the case of the RAR Bair, you can read this move and FF or AD to the ground and then Powershield or crouch. DK is slow on his aerials, and you exploit his weakness by shield grabbing/ jab grabbing.
Like around :48 when you came up for a Dair and he went for a Bair and missed it. If you quickly airdodge towards the ground he's a sitting duck. Not that you did this, but don't try to land an aerial behind DK so you can dodge the shield grab because it rarely works due to his size.
You don't really have to know this to beat the DK you were up against, but it's important to know when you play good DKs down the line. The biggest problem with peeps is getting comfortable with the strings.
Other stuff...make sure you learn to tech the Cargo > Stage Spike, because you can footstool them for a gimp.
If they do Down B near you, you can SHFF to a buffered UpB; it will always work if you time it right.
Don't get greedy with the aerial strings, or you'll eat a foot in the face. The worst places to attack DK outside of a string is from below and behind. From below, you can usually bait a dair however so it's not all bad.
I didn't see you do it or your opponent, but when you ledge hop to fireball or someother attack, a DK can absorb the hit the punish with a Big punch, fyi. The same goes for the UpB, but it isn't as big a punish and is mostly used for a safe means to return to the stage.
People say never roll behind peeps, which isn't always true. But DK you do in fact never want to roll behind unless you time his Fsmash perfecly, DK can punish with a lot of things.
Use luigi's Slipperiness! If DK is above you and you are on the ground and he tries to attack you, you can shield and slide > shieldgrab. If you don't know what I mean by this I can show you a vid.
He didn't shoguard...if he did I'd give you tips on dealing with that, unless you don't know what shoguarding ish.
Use tornado to ruffle DK's fur, but be careful as he can shield grab that sometimes.
Overall decent, just some finetuning for future matches against DK and you'll have that matchup down.
Maybe I'll rate another video later
.
Watch the platforms with DK, as you're never safe when he's below you.
