I've had an interesting thought about the Shadow Crystals... or rather, about their bearers.
Chapter 5 secret boss spoilers below - ye've been warned.

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I've had an interesting thought about the Shadow Crystals... or rather, about their bearers.
Chapter 5 secret boss spoilers below - ye've been warned.
THEYRE GONNA SAY IT THEY'RE GONNA SAY I-
....Oh.
"Failed Dreams".......
Now, this couldn't have anything to do with the previous secret bosses could it?
Jevil, who saw the whole world as a game.
Spamton, who wanted more than anything to be free from the Knights control.
The Roaring Knight, who wants to destroy the world, to carry out the prophecy fully.
Gerson, who gave the shard freely, not needing it since he is free from the prophecy through death.
Mad Mew Mew, who wants to live the way she likes no matter how her body (or anyone else) feels. The last secret boss.
Hmmmmmm........
Deltarune Royalty Theory
I wonder if the reason why Seam thought the roaring knight was unbeatable and that the chapter 3 crystal was impossible to get had nothing to do with how strong they are and instead had to do with the fact that the knight is (presumably) the main antagonist and cant be defeated yet in order for the prophecy to transpire correctly.
Its why Seam says “Fate is approaching… and it is not on your side.” in chapter 2. they meant that literally. us encountering and losing to the knight was essentially guaranteed to happen because the prophecy said so. (that itself should have been suspicious to us bc so far every shadow crystal holder has been an optional battle that fate really has no say in?)
Its probably why Gaster even took notice of what we were doing in the knight fight and is basically like “????? you’re supposed to lose here what are you doing. i mean, i wont say im not interested but it definitely says here that you’re supposed to lose.”
I mean, even when we beat the knight, the knight technically doesn’t even lose. all that happens is susie chips the knight’s sword. then the cutscene plays out the same and ralsei is very upset that we weren’t able to avert the prophecy.
we essentially managed to use a technicality to change how events were supposed to go down by losing but at the same time doing enough damage to actually get something useful out of it. “going between the lines” as gerson says.
DELTARUNE CH5 SLIGHT SPOILERS!!
hey so. Guys. We have been willingly giving a singular shopkeep broken dreams which are an inexplicable power in the Dark World right? For five chapters. To a character WHO USED TO BE FRIENDS WITH JEVIL AND IS AS WELL KNOWN OF A TRICKSTER. And it's not like they have done anything to dissuade that (other than being a cozy and friendly face).
Seam keeps saying they are going to make something incredible and VERY interesting, but it's not a promise of greatness for US in particular. What if Pink ISN'T the last secret boss?? What if SEAM IS??
the 7 Flying Aces were mentioned in Chapter 1
7 Flying Aces
the Japanese translates to: "Everybody wants to be red, so there's no blue, yellow or pink."
in Chapter 3 and 4, the 7 Flying Aces are coloured blue, yellow and pink. there's also, of course, another blue Rudinn, in Castle Town.
the colour choices are a reference to the Power Rangers: who are coloured red, blue, yellow and pink.
Shadow Crystals
Rudinn Ranger could be alluding to Shadow Crystals, too.
if you assume they're referring to in-game items the only real option for "divine gems" are the Shadow Crystals- this is less strong in Japanese, where the gems are described as "beautiful", without any religious connotations.
best secret boss
The Air Crackles with Freedom
jevil
spamtom
ERAM (I don’t count the knight since the knight always shows up)
The Hammer of Justice (Gerson Boom/Old Man)
Pink (Mad Mew Mew)
what do you make of what the shadow crystals show when looked thru? How would that tie into the idea of the crystals being a manifestation of light/hope/determination/dreams?
I feel like it works together pretty well?
In the Dark World, the Shadow Crystals consistently show a vision of the Light World. Which makes a lot of sense if you assume they're some sort of manifestation of Light.
Light/Willpower/Determination/Hope is the thing that will change these worlds back into the mundane ordinary locations Kris can see through the Crystal.
The one exception is in Chapter 4, when Kris is in the same room as part of the Prophecy, it remains unchanging even when looked through the Crystal.
...Because the Prophecy is supposed to be so inevitable that no amount of Determination or Hope or Light could hope to change it. Obviously I think (or at least hope) the story of the game is about finding some way to change that, but this is what the metaphysical rules of the world indicate at this moment.
Now, the visions it shows in the Light World are a lot more... cryptic.
But I think the most likely scenario right now is that these are visions of the future; Kris losing their hand, Susie being angry with Kris (maybe because she found out they're a double agent?) and Noelle... oh god, who knows?
Considering Determination is already known to have time-manipulating events (that was the whole point of 'Undertale'), maybe creating Premonition Crystals could also be a part of it?
It might also be that all of these Future Scenarios are going to be themselves a result of Willpower/Determination... maybe the Player's? Because they generally seem to turn out bad for Kris. Maybe even glimpses into the future events in the Weird Route, considering the Vibe of the Noelle Vision, and Chapter 2 and 3's Shadow Crystals' connection to the Weird Route, and that the whole Route is about a twisted expression of the Player's determination.
Even if it's not specifically all from the Weird Route, I think there might be a thing of... the balance between Light and Dark. In the Dark World, Shadow Crystals just show you the Light World, a fairly neutral vision of reality. But if you try and use this physical manifestation of Light in a World of Light, that's too much Light, it upset the balance, and so it gives you visions of dark and uncomfortable realities and demonstration of Determination gone wrong.