So basically i am writing a full scale essay on Reverse Undertale Theory and as for me the Sanctuaries are the second in accuracy to following this theory. So shortly the main aspects are:
- The three Sanctuaries are by far the largest Dark World territory (both combining them all and in particular), while Waterfall by far is the biggest Undertale location.
- The Sanctuaries, as usual, come in reverse — The Dark Sanctuary is supposed to represent the place where you fight Undyne, that's why Gerson is the earliest of the secret bosses (all other bosses are only accessible after you reached the last location of the Dark World excluding the Shadow Mantle holder but you can say the Sword Route can be completed after the Green Room is frozen, too so that can count)
- The prophecy on the walls corresponds with the documented history of war of humans and monsters and lore drop on souls on the walls of Waterfall perfectly
- Everything in Undertale that could have been amplified was amplified in Deltarune, such as the piano puzzles which are corresponding to that one piano puzzle from Undertale, and contrary to the original puzzle which was a simple author gag piano puzzles have a big plot significance in Deltarune
- Jackenstein which acts like a mix between Napstablook (who lives in Waterfall and is shy and with a low self esteem), Temmie (who speaks erroneously) and Mad Dummy (who wants to chase you away and uses understudies — but marching pumpkins, unlike minidummies, act cosmetic-like)
- Waterfall ends with Undyne chasing you out of it, and Hotland begins with her collapsing and going away after you give her water. TV World (which is Hotland in this theory) ends with Undyne being abducted by the Knight with us chasing her.
WHAT DO YOU TWO THINK