going to need to finish the secret routes before I make any kind of comprehensive analysis, but some thoughts on the new Deltarune chapters now that I’ve finished the main story of chapter 4:

• Sans’ overt use of innuendo with regards to Toriel in chapter 1 (“i already "befriended” your mom last night", complete with scare quotes) naturally lends itself to reinterpreting the finale scene of chapter 4 as also being innuendo; Kris covers their ears while Sans and Toriel make dialogue sounds back and forth at each other because THAT’S THE SOUND OF THEM HAVING SEX!! hehe. crude yes but i am using this as my justification to think of chapter 4’s events less literally:
• a fire extinguisher declares itself the “most important” object in the church (in an unusually explicit identification of darkner with object, another nearby character points out to us that this guy is in fact a fire extinguisher just in case we couldn’t figure the joke out visually) - in Susie’s re-interpretation of the dark world, this fire extinguisher proves its importance by providing the heroes with the code to get into the locked church hall. combined with Susie referring to the darkness spilling out of the locked church as “smoke”, one gets the impression that what we’re ‘really’ witnessing here is the church being set alight?
• the Titan heals itself by absorbing its own spawn - bringing to mind Cronus, the Titan who swallowed his own children. thus it seems that “Titan” is more than just an evocative name, and we can look to the Titans of mythology for further understanding…
• as such, is Jackenstein’s name meant to invoke another mythological Titan, in the sense that Frankenstein was “the Modern Prometheus”? further fire imagery abounds: as a jack o'lantern, Jackenstein’s body is lit up from the inside by fire in the same way Frankenstein’s monster was imbued with the divine fire of life, which the mythical Prometheus gifted to the first humans - and just as Kris’ own soul also glows with divine light, which becomes the primary way of fighting back against the Titans.
• (no doubt the reference to Frankenstein also ties back to the opening of chapter 1, wherein we are invited to cobble together a “vessel” from human parts - a title referenced once more in chapter 4’s prophecies)
• the church’s candles transform into ghosts in the dark world, surrounded by iconic depictions of Japanese spirit-flames - further reinforcing chapter 4’s association between souls and fire.
• thinking back to chapter 3, the secret S-Rank levels tell us that “the forbidden path began with ice magic” - positioning abuse of the elements as a kind of original sin, much like the transgression of the mythical Prometheus. obviously “ice magic” is in stark contrast to the above symbology, but still it bears mention… the Dreemurr family were of course in possession of their own “fire magic” in the original Undertale, which we have thus far yet to encounter in the sequel; and I wonder if the fact that Dark “Fountains” produce “smoke” is supposed to suggest opposite elements being superimposed or at least contrasted in some way?