MOTHER 1, Deltarune breadcrumbs, Stanislav Petrov, and the time loops (speculation).
This small idea came to me after reading the OG Mother 1 description when this clicked for me. Also goes off into a rant. Bread Crumbs. In-game description: If you follow them, you will return to the place that you started.
Symbolically, MANTLE in Chapter 3 are the breadcrumbs. If you follow them, you will find the Weird Route.
Completing it will give us power, but Deltarune as a story ceases to be. No game to choose within. Think of it as like that chart that was shown in EmpLemon's youtube video Stanislav Petrov | Never Ever E4. I am going to steal a lot freaking stuff from this chart. Gaster's CREATING A NEW FUTURE WITH YOU is already happening. The SOUL's insertion into Deltarune could technically be considered a world altering event already, as the Deltarune we play might not even BE the original Deltarune that existed within Toby's mind.
Deltarune and Undertale have always existed as this Oroboros state. Deltarune as the fever dream and idea came first, but Toby wanted to first test himself by making a game. (I'm pretty sure he would've used Earthbound as Undertale's supplement if he were to make Deltarune back in the 2010-s, it was quoted somewhere idk) Undertale was made and it blew up skyhigh. If Undertale didn't sell well then Toby would have released 'Deltarune' as concept art as quoted by his Undertale Kickstarter page. Gaster was manifested in Undertale first conceptually. I believe he found Toby's Lost Dream of Deltarune (2012), and he became obsessed with completing it (SURVEY_PROGRAM 2018). Therefore he hodgepodged everything that he could salvage and created a device that connects us, the people with the power to change fate, to create the future of his Deltarune. Our choices not mattering are most likely hundreds of failsafes implemented in order to have as little chance at annihilating his work as possible. He needs us to keep his Deltarune running, but he also needs us to follow a beaten path, otherwise the whole structure of Deltarune, the story, the game, the machine, will fall apart. "EVERYTHING WILL FALL APART!" Ralsei CH5 quote on what happens if he does something that deviates from the Prophecy. "THEY ALL [Fall Apart]" (Different Snowgrave fangame quote from Spammy Whammy, but it fits so I put it in)
"The original game beneath the surface." MANTLE, where you could choose your freedom. Unaltered by Tenna. Mancountry. Unaltered by Gaster. That is what we will find in that place filled with nothing but evil. Not just Gaster's spooky Meat Factories, but the original Lost Dream.
Going back a little, Petrov parallels the Player, because neither Routes are building towards giving you true Power. You will either let the big bad Tragedy happen and try to mend things from there (as it happened in Undertale's Pacifist Neutral Route, Flowey even quotes your choices not mattering) [Power with no Agency], or you give all your power to Noelle, who does have Agency over her life, but little power [Agency with no Power]. Both routes are a paradox essentially. We haven't been able to complete either of them, so they might give you the necessary component that you lack to gain full power, but idk. That's too high concept even for me currently.
Perhaps, and I do say perhaps, eggman's clopen inbetween eggs + the ShadowCrystals will give us a big enough "nudge" to change something bigger than what was planned for us. One can only dream after all.
