I wonder if we'll ever get a undertale 2, im pretty sure Toby doesnt want to ruin it (he barely wanted to sell merchandise), but i think he mentioned something about an upcoming new game. Also the myster about Gaster is still loose, and just a bunch of speculations. (maybe finished through patches though)
All my youtube reccommendations are undertale related stuff, im watching all theses story clarifiers, random facts and speculation theories. 2deep. If theres something i like in videogames, its when a story has a loose end with speculations, or a story that has to be dug out. I never figure them out fully myself, but its super interesting when listening to youtubers reveal them.