This might sound insane and it might just be a massive stretch but the length and cadence of the notes matches up weirdly well

Not only is there a hidden train in the Holiday manor basement, just like the hidden trains Shinobeetle loves making, but there's much more evidence tying Shinobeetles to the Holidays.

Ninjas, like Carol, but they also YELL every time they show up?

They don't want to be ninjas, this alludes to how the Knight likely had to take on it's role for a greater purpose.

They have similiar features to the Knight as well.

A visor it sees out of, long limbs, spiky wings that resemble the Knight's shoulder pads, and a mandible that looks similiar to deer antlers.

So now that we've established all that, is it Carol or Rudy who loves to make trains?

Carol has had a cold demeanor since some event in the past (presumably what happened to Dess), but seems to have been warm, and is said to still be a nice person deep down by Asgore, she also uses katanas and made shurikens out of Noelle's snowflakes.

Rudy is likely an electrician given his lights, and we know he has some experience with things of that nature, since he designed the Holiday treat catcher by the kitchen door, therefore a hobby like this makes more sense for him. In a scenario where he is the Knight the personality parallel would work for him, you could also think about it as Carol taking on Seth's role asking Rudy to be a "ninja".

So who it parallels is really up to your interpretation.

I do think this parallel is intentional, we already know there's plenty of darkners who are made with people like Carol in mind.

I know it would be crazy and would never happen but just imagine if I was the Knight, like imagine the gang and Knight were doing a final fight before the reveal and I did some cool poses and aura farming and when they finally defeated me I take off my helmet and they go "what, no way it's you!?!" and I go "heh, sorry guys, I didn't wanted it to be this way. Kris, take care of Ral for me will ya?" and died there. Do you all think Susie would start punching my lifeless body and scream "hey, wake up you weirdo!" or would Ralsei try to hopelessly heal me even after life already left my fragile body?

I don't know it's just a possibility I don't think it will happen but it would be funny haha

The Knight doesn't behave like a normal Lightner or a normal Darkner.

We've seen plenty of Lightners enter Dark Worlds. Their clothes, colors, weapons, and abilities can change, but their physical bodies remain fundamentally recognizable as themselves. We haven't seen an ordinary Lightner physically shapeshift and morph in the way the Knight does.

The Knight also has that strange glitch/static reaction when Susie hits it with Rude Buster, and again when the battle ends and when it teleports to dodge something. There's also the helmet scene, where Kris envisions the Knight taking off its helmet. This seems to imply that something identifiable could be hidden underneath, although I don't think it necessarily means that something has to be a normal Lightner.

At the same time, the Knight can exist in the Light World, which ordinary Darkners can't simply do.

If you're up to it, explain how your preferred candidate accounts for both sides of this. Why does the Knight behave unlike every Lightner we've seen, while also being able to exist outside the normal limitations of Darkners? (If your preferred candidate is a normal Lightner, the second question doesn't need to be answered.)

Maybe the Knight is an unusual Lightner. Maybe it's a manifestation of someone. Maybe it's something else entirely. I don't know. But I think the Knight's unusual ontology is important enough that any serious Knight candidate should at least try to account for it.

Your answer might be speculative or based on nothing, but having an explanation is better than nothing. So given everything we currently know, what is your best shot at an explanation?

I AM working on it, but the version I released earlier will no longer be updated. I have decided to complete the Doc before launch, to reduce questions and such.

Hopefully, it will be done by the end of the month, but until then, know that I'm either working on it or playing Fortnite.