You understand the character, so I'll go into specifics.
- Actually, one basic thing. Use bair to momentum cancel, you might have lived at (1st) 2:08 and (2nd) 1:23.
- Don't use fsmash so much without mindgaming it in some way (1st vid and the PS1 matches)
- Implement boost pivot grabbing, you had several great opportunities to use it: (4th)0:01-0:12, (3rd) 0:20, (3rd) 1:34
- Speaking of which, get the chaingrab down. If they escape, it should be because you didn't grab soon enough, not because you threw in the wrong direction (there's a comment on the 3rd vid anyway; you buffer the walk/grab, not the throw)
- Don't get predictable with phantasm as a ledge option. If he's clearly standing in the middle of the stage, he's expecting it, like at (1st) 1:28
- Don't use firebird as an attack or as a horizontal recovery, it's astounding how Seibrik didn't punish you for it (1st) 2:54
- Occasionally, you SHDL'd too high. Just relax I guess. It needs to be consistent.
- Don't phantasm back onstage when high, that's easily punishable (especially for MK). Yes, I know he eventually started spamming tornado at stage level, but you did this beforehand.
- Your usage of reflector was somewhat incorrect. If you're using it on stage, then only do so with a retreating SH. Don't use it offstage if you don't have a second jump... or at all offstage, lol. The one exception is ledge drop > 2nd jump > reflector, but when you did do that you went too far onstage and were punished. Either regrab the ledge when doing that or barely go onstage so as not to get punished. It's a pretty bad option anyway.
- Use dair out of your CG if he's clearly going to land onstage. You can techchase for potentially more damage as opposed to usmash.
- You could have IAP'd a bit more, but meh.
You're good, but as always can improve.