Catbill AU
Inspiration: A post by @writing-prompt-s shown here
What it's about: After escaping Stan’s mind, the Axolotl gives Bill several options for his new body and Bill chooses to become a cat. He’s dropped off at an animal shelter somewhere in Northern California and much to his surprise not long after, Dipper and Mabel, now 18, show up to the shelter looking to adopt after the death of their previous cat. Bill grins and immediately starts acting friendly with them to convince them to adopt him. They think the cat looks a little odd but he’s friendly enough and seems to like them well enough, so they take him. He’s a troublemaker and a biter, not to mention seemingly just a little too attached to Dipper in particular, but he turns out to be a great pet.
But one day Bill slips up. Dipper happens to catch him muttering to himself about something and recognizes the voice. He eventually gets the cat to admit who he is, and Dipper and Mabel agree it’s best to keep Bill as their pet. After all, the alternative is to release him to the streets which is potentially more dangerous. And besides, even knowing it’s Bill, he’s still a good pet. That is… until Dipper incidentally learns that Bill retains his transformation abilities and can take the form of a catboy who continues to be extremely attached to him.
At some point, Bill casts a spell that also turns Dipper into a cat. He can turn back into a (catboy) human, but only when Bill decides he can.
Let me know if you're interested in this AU! ^_^