Long Post Warning!
My laptop decided to shut down so I lost everything I had typed out previously
~~~~~~~~ General Tips ~~~~~~~~
I see lots of SH Fair / Forward momentum PK Fire (good, but the opponents will see the pattern after a bit... have to keep changing it).
I haven't tested these, but I just came up with the ideas:
1) - only works if opponent falls towards you after being hit with PK Fire... I think.
SH PK Fire forward -> dash forward while they're stunned / in the air for a second, spot dodge as they're landing and follow up with a SH Nair or something.
2) - Dash attack when they don't expect it... er, okay, these aren't the best ideas... I did the video section first so my concentration's a bit fried
I think you would benefit from practicing these things in general:
- Spot dodging
- Air Dodging
- Coming up with new patterns
- PK Thunder
- PSI Magnet
- Spacing
- Edge Guarding
(seems like a long list, but don't be discouraged. Once you're conscious of these while you play you should be able to start seeing improvement within 5~10 matches easily -- as long as you put in the effort to break the old habits and work towards these.)
~~~~~ Examples from Videos ~~~~~
"Metroid (Lucas) vs Itakio (Marth) 2"
PK Fire too close / punished.
0:48, 1:07, 2:14,
2:59 - If you had spot dodged instead of using PK Fire, you probably could have made a hit.
(2:20 shows a nice backwards SH PK Fire Waveland... do more of that!)
Drop from a platform with an aerial.
1:35 - I think Nair / Fair > Dair in that situation. A lot less landing lag = easier to chain attacks / attempt a grab / spot dodge.
Air dodge.
1:39 - A well timed Air dodge would have gotten you back onto the stage.
3:03 - Don't stop to use PK Thunder if you don't need to during recovery, as an air dodge probably would have worked there.
Edge guarding.
2:00 - You used PK Freeze, but instead try to latch onto the edge as Marth is working on his recovery, and when he uses up+B, use the invincibility frames from rolling onto the stage to avoid damage + edge guard. (not 100% sure it would work... I'm thinking of Melee days).
2:01 - Instead of rolling back from the edge as Marth starts to get on, try staying where you are and spot dodge -> attack with a faster move.
Spot Dodging.
3:12 - If you had spot dodged instead of shield, you likely could have hit.
Metroid (Lucas) vs Jaydo (Pikachu) 1
I don't have much experience against Pikachu, so I'm not sure if it's possible to spot dodge Fair / Dsmash and such... if not, disregard part of this.
2:20 - Spot dodge the Fair, hit before he goes into Dsmash.
3:02 - spot dodge the close range head butt -> send a PK Fire / dash attack or something after Pika.
3:08 - another chance to spot dodge.
There were opportunities to air dodge as well, but I'm not going to point them out.
Metroid (Lucas) vs Itakio (Bowser) 1
Air dodge.
1:45, 3:07
Edge Guard. (spot dodge + hit back)
1:54, 3:16
PK Fire too close / punished.
3:03
Metroid (Lucas) vs Jaydo (Pikachu) 2
0:12 - You can tell right away that Pika's going for the Fair -> Dsmash combo that he spammed from the other match. spot dodge the Fair and hit back (if possible).
1:28 - Pika had low %, so a SH Nair could have been better in my opinion.
2:25 - PK Fire too close.
3:19 - Air dodge.
3:27 - Don't trip

I've also heard that DI'ing down during Pika's Dsmash helps keep the knock back horizontal when you're sent flying.
Metroid (Lucas) vs iCraq (Marth) 1
PK Fire too close / Punished.
0:14, 0:17, 0:35,
Air dodge.
1:19
It looked like you weren't really sure how to handle the stage's design (shorter length, platform in the middle)combined with Marth's speed / range.
~~~~~ Closing ~~~~~
I know all of the things I mentioned are much easier said than done (especially when analyzing game play from videos), and you're honestly probably a better Smasher than me, so I guess I'd take all of this with a grain of salt if I were you, since I might not know what I'm talking about in parts of it compared to others. (see: Smash n00b title / post count :embarrass)
~~~~ *Edit* ~~~~
Nair is awesome, seriously.
But PK Freeze isn't, so, you know, stop it

Tether recovery might be a good thing to learn how to use as well - more mind game options.