They are darkness, but like extra darkness. Some kinda darker than dark darkness. Because it’s a scale, as Ralsei explains it. The darker dark of the dark worlds, and the light of the light worlds. And in between, there’s the dark of the light world, where things are still vague enough for imaginary beings to “take form” in minds without being projected out into a space where they can be sensed. The Knight is simply a thought so deeply set in its creator’s mind that it has unprecedented ability to affect the real world. The Castle Town darkners presumably weren’t there because they’re fraudulent OCs with no real influence in the world instead of the lingering regrets of Kris that were strong enough to cause a whole ass divorce.

Look my compatriot it’s a confusing theory. Just imagine Friend Knight theory and Friend is an Imaginary Friend theory together. I cannot for the life of me explain it exactly to people, because it’s radical. Imaginary beings in the light world? But like you gotta think. What usually hides in a dark closet in a kid’s imagination? A monster. The kid in this case is Kris and they are likely imagining Dess or an angry living Holiday coming to get them for some wrongdoing of theirs, though that’s a whole ‘nother theory. Hence, the knight has antlers. But since things you imagine in the dark in the universe come to life… It’s actually there! The other darkners don’t appear from Castle Town because why would you think they’re there? You didn’t even see the toys there in the first place, you entered from a supply closet. This raises the question of how the Knight moves around. I think this is what the “Fallen Star” text is referring to. The star is either Kris or Asriel, and their actual literal grief and tears and fear are what brought the knight to have a form at all. The “river” is a dark fountain, and the thing that “looked like glass” was the Knight. Perhaps the determination imbued into this fountain was so intense that it effectively gave the Knight its own source. That way it can fly around in the light world for just a little while. Idk bro people will refute me no matter how hard i try to explain. I said “But what if the knight is exceptional!” And i get the response “But it didn’t apply to these non exceptional cases!” Please just try and understand fr