Okay, so, with Chapters 3 & 4 coming next month, this is my chance to go over every prediction I've made so far.
First: kingdoms and secret bosses.
I originally assumed the secret boss would be the book of hymns, because Jevil and Spamton Neo were both confronted in the bottommost corners of the rightmost ends of their kingdoms. However:
This, of course, would depend on the next kingdom spanning the rest of the living room and not just the tv itself, and I was doubtful before that the next kingdom would be entirely tv-themed, but Cyber Kingdom did only borrow a few details from anything else around the computers.
That said, I saw a post pointing out that the trend may be items that were always going to be cast aside. I had my doubts about this one because I figured rules cards would get more neglect than jokers, but this could still have merit.
Both 1 and 2's locations were also directly under the rulers' own battle stage, so if the tv is the next castle, then the next secret boss might actually be a vhs tape left inside that player, such as a home video, or even something hidden under the tv stand itself.
I still think the book will be an important character somehow, but I'm tentatively withholding my assumption that a hymnal Darkner will have the next shadow crystal.
(Speaking of which, where did those shards come from? did Dess wear glasses? And is this "mantle" as in the shelf above a fireplace, or "mantle" as in a cloak? If it's supposed to be clear like glass, could it be some kind of plastic wrap, or tape? If it's tape, are we supposed to start piecing the crystals together?)
Second: character arcs per chapter.
Back when the first chapter was released, it seemed to me like a recurring theme was kindness– for example, Susie's character arc. And in chapter two, though it didn't match up with playing in shooter mode against Spamton Neo, it seemed to me like Noelle had a character arc themed around bravery. Learning to stand up for herself despite her phobias and anxieties. Assuming Determination is reserved for last, Kris opening a Fountain may open discussion about justification, and Toriel's phonecall suggests that we may be joined by Undyne or Napstablook either that night or the next day. Toriel may not necessarily be our other party member this chapter, but instead more like Berdly.
Right now, my prediction is that the order goes kindness, bravery, justice, patience, perseverance, and finally, determination or whatever other trait has been theorized to be attached to red– which may be something meta-related.
This one is based on the windows pages. The track playing in the basement leading to Spamton Neo is called digital roots, which is when you add a number's digits together until you get a single digit. 18 = 1+8 = 9 and 36 = 3+6 = 9, and both are even numbers, meaning they're both divisible by 6 and 9. Which are numbers associated with Chara and W.D Gaster.
This one may be a stretch, but there were also 51 windows total, which is divisible by 17 (another number associated with Gaster), has a digital root of 6, and the rarecats jumpscare was the same face you have a chance of seeing in that basement. The face with eyes like Spamton's shades.
By itself, this could all mean nothing; but if we get another puzzle like the windows, I'm betting on the answers being 54, 72 or 90– all divisible by both 6 and 9, or even numbers with a digital root of 9.
Fourth: Kris' motivations and Toriel.
The secret bosses are all optional, so I don't think Kris could be explicitly looking for the next one.
There could be any number of items Kris wants to become a Darkner, either to contact them or recruit them...
...this could've been done to prove the existence of Dark World to Toriel if they were involved in Dess' disappearance.
We don't know yet how much Kris knew before we were assigned to them, or even why we were given control over them– and either they can't tell us themself, or they've been trying not to. Because they have no reason to actually trust us.
But if Dess got lost in a Dark World somewhere, and Kris witnessed it, this could be their way of showing they didn't just have a wild imagination as a small child.
Which means that we might find out from Toriel how it was reported, and whether she divorced Asgore because she blames him for failing to find her. Even if he does know more, it could've been too unbelievable, so there's a chance that this is Kris' chance to prove to her that Dess' disappearance was abnormal.
Remember when he showed up in Cyber Kingdom? On his own?
...I think he's gonna have his hat on again.
I mean, sure, he does look strangely like a Dreemurr, right? What would Toriel think of him? Would he want to explain the resemblance in front of us, or in front of Kris?
...But how would he know to hide his face?
Sure, he seems to know where new Fountains appeared or how to get there, but should he know Toriel's there?
There may eventually be an innocent explanation, but Ralsei will know more than he should and players are going to get suspicious.