angel hunters series book one: dreamscape to apocalypse

Dreamscape to apocalypse is a Gravity Falls fanfiction set in the middle of an apocalypse; but the thing is is that the apocalypse was not made by bill cipher. This world wide apocalypse that leaves everyone baffled sends an autistic detective, and a Girl who'd been raised by an imp, to the town of gravity falls because despite its apocalyptic nature it is the one place on earth free from the effects of the apocalypse. There they meet bill cipher, who the current owner of the mystery shack refers to as a dream nacho with a top hat and he is trying to trick them into removing the dome of weirdness so he can create a global Weirdmaggedon amidst the chaos of the existing world wide apocalypse.