"fell into his creation" / W.D. Gaster fell into his creation -> motif inside Undertale. we can't even know for sure how this statement turns into a claim because we don't really know what the creation is.
In Undertale
The Underground is a creation / The Underground is the creation of someone inside the Watsonian cosmos of Undertale or Deltarune -> you can fall into it. if you're one of the six previous souls, you vanish without a trace. everything about Gaster seems so weirdly metaphorical, and there has to be something in there.
Gaster sealed the monsters underground; they remember it wrong
