Yknow how in pure darkness you hallucinate?
Thats Toby’s inspiration
Your brain hallucinates, taking things from your mind.
The dark worlds, is where those hallucinations become so powerful they become physical, but really it’s your hands feeling what’s not there.
The dark fountains create that pulse of darkness “that gives this world its form,” because it makes the hallucinations more vivid.
Too, all the memories of the real world are part of the dark worlds, like the old classroom, its connected to the closet (main Dark world) by the gate you go into at the start of chapter one.
You seal the fountain in chapter one, removing the dark world from that classroom, based off of its contents. You can see based off the environment in all the chapters