Yeah... I have yet another theory... It's about the creator of the dark fountains... But like, in Undertale... 'Cause Gaster doesn't have a body to fit in the Roaring Knight's armor... Also, my writing might not make much sense... sorry about that...
So, everyone knows who W.D. Gaster is, right? If not, he is the "original" Royal Scientist from the game Undertale. When he was making the CORE (ya' know, the big power-plant thing in Undertale that is found in Hotland), he slipped and fell in, shattering him across space and time. Of course, there are some people that remember him- Gaster Followers. These people- actually, this will take a long time to type if I type in his full backstory. Just search it up. Anywho, I have a theory. A GAME THEORY- wait is that copyrighted? *checks* Nope. A GAME THEORY!! So, the followers mention that Gaster shattered across space and time, right? Yes. Did the experiment (entry #17) have very low to no light? Yes! But what does that mean? When Gaster fell in, he (maybe) dusted when he fell in the core, spreading him across "space and time". What did we learn about dead monsters in the dark world? They become darkeners and are still "alive". Gaster must've created a dark fountain in the Undertale universe. When Gaster fell across "space and time", he fell into the dark world. The dark world exists in Undertale and Gaster was the first to create it. If you don't believe me, just remember Deltarune is an anagram AND a parallel universe to Undertale.
