Spoiler: Knight identity
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Indeed you are correct, Queen and Chaos King not recognizing Kris is a big wrench in that theory, as I've said before.

At the same time, there are other things to consider: namely what "Determination" is in Deltarune. We don't know if its the same thing as it is in Undertale. Because if it is, using Determination would make the monsters melt. Which would severely limit the amount of people who can repeatedly make Dark Worlds. There would have to be another human in town somehow unknown to everyone living there making things happen if its not Kris when they take out the heart.

But Deltarune is a different universe with seemingly rules so.....if its not Kris then it has to be one of the monster lightners doing all this. We can only then narrow down our suspects through logical elimination of means, motive and opportunity.
-it can't be Toriel, she arrives at school the same time as Kris, so she wouldn't have the opportunity.
-Alphys does seem have to a motive: make Dark Worlds and get cool videogame stuff, but then why not go to her own room of videogame stuff and go dark world that? makes no sense. Can't be Alphys
-Its not Susie, Berdley or Noelle as they are all surprised by the Dark Worlds and have genuine reactions to their existence.
-it can't be Mettaton, they don't go out of their home ever in this world, and would've been in the computer Dark World if they knew.
-Undyne? Hm. we have two opportunities to inform Undyne about the Dark World and each time she doesn't believe us. she is a cop so she can plausibly move more freely about than most. despite Toriel calling her, she doesn't show up at the end of Chapter 2. She is an incredibly determined person and doesn't like it that nothing happens in this town. is Undyne the Roaring Knight? she has the means, she has the motive, and more opportunity than most, unless we think she is too busy with her police job?
-Papyrus doesn't seem to come out of his home either
-Goth Catti seems interested in the occult but she works a diner when would she have the time?
-the snowguy and monster kid seem scared and curious about the southern door, so it can't be either of them why be curious about that when you got the power to make Dark Worlds?
-Jockington? no is always around Goth Catti, so there would be two Knights in that case, makes no sense
-Asgore......Asgore......lets see.....his flower shop is failing, and he is divorced....so both motive and opportunity. its means that I'm not sure about, its a small town anyone can reach the school or library during the night, kris sure can by just walking around, so it comes down to whether he knows enough about the Dark World to do it, which we can't say for sure, but....his back flower room with the seven flowers arrayed? thats begging to be a Dark World, so same problem as Alphys: why not go into that back room and make a Dark World there?
-the next suspect.....is Sans. He certainly knows more than he is saying, has knowledge of Dark Worlds and the doors and such, but there is a problem with that, and a wholly unique one: he might be a Darkner, which makes him unable to open a fountain because only Lightners can do that. (the reasoning why Sans might be a Darkner are: he has blood but also casts magic, which Undertale monsters don't have they just fall to dust....but Deltarune Darkners do know what blood is since Lancer threatens the Fun Gang with a blood-based threat, and Sans uses a magic door to his room that is similar to the ones we use to traverse other dark worlds.) meaning Sans is potentially eliminated because he is TOO involved in a way.
-The Mayor? maybe. we haven't seen her yet. she is supposedly very effective and busy but.....
-It can't be Pizzapants, he'd want to Dark World Pezza's to screw over his coworkers, like immediately.
-the rest of the townsfolk are too minor to really suspect them.

So current Roaring Knight suspects are: Asgore, Undyne, Mayor if we're discounting Kris.

now another theory might be that its simply that Goner we made at the beginning of the game, but thats a bit of a copout since that Goner doesn't really have anyone controlling it, and some Goner just phasing in and out of reality to do all this feels cheap, because there is no other way to really guess that.