There's a peculiar flower called Chrysanthemum, which translates from Greek as "golden flower", and is often depicted as Sun in Japan. It blooms in autumn and is native to East Asia.

In Japan, the chrysanthemum is a symbol of the Emperor and the Imperial family. In particular, a "chrysanthemum crest" (菊花紋章, kikukamonshō or kikkamonshō), i.e. a mon of chrysanthemum blossom design, indicates a link to the Emperor; there are more than 150 patterns of this design. Notable uses of and reference to the Imperial chrysanthemum include:

• The imperial crest of Japan is used by members of the Japanese imperial family. In 1869, a two-layered, 16-petal design was designated as the symbol of the emperor. Princes used a simpler, single-layer pattern.
• The Chrysanthemum Throne is the name given to the position of Japanese Emperor and the throne.
• The Supreme Order of the Chrysanthemum is a Japanese honor awarded by the emperor on the advice of the Japanese government.
• In Imperial Japan, small arms were required to be stamped with the imperial chrysanthemum, as they were considered the personal property of the emperor.

Asgore was a royal figure in Undertale, so that status may be regained as an Emperor, using The Chrysanthemum Throne - the Sun. The sun shown in Ch5's trailer is the golden wedding flower, a chrysanthemum. Since current season in Hometown is autumn judging by yellow trees, it's a perfect opportunity for Asgore to grow other chrysanthemums.
Then, the Inferno of Jealousy will be caused by chrysanthemums. Either the "wedding" flower because Asgore cares more about the other of its kind (typical rich oligarch's kid trope), the new ones because there's someone higher than them that looks the same, or even all of them since Toby frequently puts the dramatic "two sides of the coin" in his games, letting you experience the hurdles of both sides.

Another thing (probably a coincidence tbh) to point out is the flower's scientific classification:

Clade: Asterids
Order: Asterales
Family: Asteraceae
Subfamily: Asteroideae
Tribe: Anthemideae
Genus: Chrysanthemum

Notice the prevalence of "Aster" (from Ancient Greek "star"). Unfortunately I couldn't find any realistic meaning behind it. I tried to tie it to Asgore being the "fallen star making rivers with its tears", but it led to nowhere. So let's assume it's yet another one of Gaster's shenanigans.

Toby hinted in the newsletter that in Chapter 5 we would smile for the last time. The music from The Depths plays in the lake near Hometown, and Onionsan never returns after mentioning it. Strange things are happening in the lake, and there is no explanation for them.
However, I have a separate post analyzing The Seven Suns in Asian culture, that tries to solve it. The TL;DR is they describe an end of the world similar to The Roaring, where every single droplet of water evaporates from Earth due to immense heat 7 suns produce, making all lakes, seas and oceans empty. Kind of what we can do on Board 1 of Ch3. I'd appreciate if you take a look at it!

What I think will happen is the flowers would suck all water from the ground using Roots and reveal the bottom of the lake. Flower King is the only place with a Dark World that'll have access to land (Kris's house, Librarby, School closet, unused classrom - all are isolated from the earth), perhaps from its basement, or whatever vines intertwine the building.

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Thanks to AstraBiolog for starting this theory.

DELTARUNE TOMORROW

World's end in Buddhist prophecy

So following Toby's post about The Sunset of Seven Suns, my friend AstraBiolog decided to look up anything about them and found something:

According to the Buddhist text "Satta Sūriya Sutta", The Seven Suns is an apocalyptic prophecy about the end of the world. The text describes that at the end of the world cycle, new suns will appear one after another. Each new sun will gradually evaporate the water in streams, lakes, rivers, and then in the great oceans, until the entire earth eventually burns.

Buddhism is heavily tied to the history of East Asia, including Japan. The Roaring and "inferno of jealousy" clearly stem from it. In ch3, in order to proceed on Board 1, we have to drink all water from the oasis, causing the entire board to dry up (or block the stream with Lancer, causing all water to still evaporate).

Mongolian legend about an Archer losing his thumbs

There's a Mongolian legend of "The Thumb Who Became a Marmot" (https://www.tellstory.net/stories/mongolia/legend/the-legend-of-erkhii-mergen-the-archer) that was based on the events described previously:

The talented archer Thumb (in Mongolian - Erkhii Mergen) once volunteered to save the world from destruction when there were seven suns in the sky and the Earth was languishing from the heat. The archer made a bet that if he failed to shoot down all the suns from the sky, he would morph into a creature that doesn't drink water, lives in holes, and eats grass. And he would also cut his thumb off, which allowed him to use his bow without missing a target. The sharp-shooting Thumb knocked down six of the seven suns with his bow, but just before the seventh shot, a swallow flew in front of him, and the arrow hit its tail, causing it to split in two, but the target remained unreached. Erkhii Mergen was so distraught that he cut off both his thumbs (according to another version, bit off) and turned into a marmot.

I believe Deltarune Chapter 5 will retell this story. The parallels could be as follows:

1. Kris is parallel to Archer. Both share outstanding accuracy in shooting (whenever we were a soul, Kris was always making perfect throws at us, be it a milk bottle or a hockey ball).
2. Archer's bet may be Kris's promise about losing their hand, or even both out of their distress. This will prevent Kris not only from playing piano adequately, but also from throwing things properly or even the ability to take the soul out forever.
3. Eating grass = eating moss. Because there's kind of nothing else to make out of it. Not drinking water may be connected to Kris's talassophobia, considering the Watercooler enemies being OP, Shadow crystals moving like water in their hand, water freezing into Ice which itself is a painful topic, etc... Heck, the Dess/Kris Drowned theories might be true even...
4. The Roaring will heat up Hometown and evaporate its mysterious lake, revealing something important on the bottom of it. My guess would be The Depths, since some ominius music plays from the lake of Hometown, Onionsan never returns after telling us about it and the Gonermaker's background (which is the depths) is sourced from an ocean. Toby hinted in the newsletter that in Chapter 5 we would smile for the last time.
5. 6 out of 7 suns were defeated = the whatever were ⁶🤷‍♂️⁷ Gaster parallels.

7 suns as optical illusion

Lastly, a fun fact. There's a news article (https://www.vokrugsveta.ru/articles/nad-kitaem-zakhodyat-7-solnc-virusnoe-foto-i-obyasnenie-chto-proiskhodit-na-samom-dele-id5817954/) about an optical illusion of 7 suns rising in China on August 18th, 2024 (which basically kickstarted this theory):

On August 18, residents of Chengdu captured seven suns in the sky with their cameras. People observed this view for about a minute, according to Asian media.
The unusual effect was compared to Parhelia, a phenomenon in which the Sun appears to have "twins" on the left and right due to the refraction of light in ice crystals in the atmosphere. But in this case, the explanation turned out to be different.
This is an optical illusion caused by multi-layered glass, said Zeng Yang, vice president of the Sichuan Amateur Astronomical Society. Each additional layer of glass creates another copy. At the same time, even with the same glass, the number of objects can vary if the viewing angle is changed.
Upon seeing the photo, the user AaweBeans recalled the Mongolian legend about an archer nicknamed Big Thumb.

There may be only 1 sun - the golden flower, and the other 6 may be reflections caused by the glass covers. We know how weird glass tends to be in the game, so it might as well create such illusion in the future. Or it might overreflect already existing 7 suns and cause the place to wither.

The question here is what Shadow crystals could help with in this situation? Will we get a 5th one, return to Castle Town, give it to Seam for a PureCrystal, which then we'll use to laser beam the sunrays? Kind of like the Last Prism from Terraria. Or create the TwistedSwd out of it and use it instead? If that's the case, what would happen without any crystals?

That, my friends, we'll see TOMORROW.

Bonus

There's a Hindu/Biddhist cultural artpiece shown in "radiation is now on youtube" video on 1:44 (https://youtube.com/watch?v=pA9uy3KdeEU%3Ft%3D104) (TW: body depictions). It appears to be either Lakshmi or Mahakali (if we trust Google's AI here), both being goddesses in aforementioned cultures.

It means Toby knows something at minimum about these. I wouldn't say it supports this conspiracy theory, but an interesting detail to keep in mind nonetheless.

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Thanks to AstraBiolog for starting this theory!

DELTARUNE TOMORROW