>>712502546
The Gaster lore most relevant to Detlarune is ENTRY NUMBER SEVENTEEN
https://www.youtube.com/watch?v=fpneLl7ohUs
>DARK DARKER YET DARKER
>THE DARKNESS KEEPS GROWING
>THE SHADOWS CUTTING DEEPER
>PHOTON READINGS NEGATIVE
>THIS NEXT EXPERIMENT SEEMS
>VERY
>VERY
>INTERESTING
>...
>WHAT DO YOU TWO THINK?

With context from Deltarune, it seems that Gaster was somehow experimenting with Dark Fountains or the Dark World, and "his creation" he "fell into" might have been the world of Deltarune
Consider this quote from Gerson in Chapter 4
>That next book, it never did get written.
>The story, it became so grand, so overwhelming,
>Some say it swallowed up the author himself.