It's been exactly three years since the monsters had been freed to the surface, and Frisk has decided to visit Flowey. They offer bringing Flowey to the surface once again for the thirty-sixth time, but just before he answers, the world becomes distorted. The next thing Frisk knows, they and Flowey have woken up to a different reality. A reality before the monsters had been released, and they aren't very friendly. Note: I have the basic idea of Underfell, so I'm only making this Fanfiction on how I understand it, albeit adding a few of my own personal twists. I also headcannon Frisk as a girl, but I will still refer to them as "they" or "them". Undertale belongs to Toby Fox. The AU Underfell belongs to... whoever thought of it. Kudos to that person for thinking of this very interesting AU.