BillDip~ You're Mine: Book 2: Two King Kingd...
This follows after book 1 of BillDip you're Mine so if you haven't read that go read that otherwise this story won't make sense!
After a couple years, Dipper has lived with Bill in the Realm that leads to all other Realms. . . The Nightmare Realm. He hasn't aged being turned into a demon and all. Mabel is now going to Highschool. She has since gotten over her brother's ''disappearance'' but she is worried because Gruncle Ford hasn't, not being able to let go of when Dipper was kidnapped by Bill, his arch nemesis. After Bill tell's Dipper what he has done, Dipper refuses to go back, currently in a cold-blooded form but Bill knows what his plans are and is in control of him. After they go back, Dipper starts to age again. . . with another being he loves so much always at his side, but what he doesn't know is this other being... is another one of Bill's evil plans.
Cover Link: https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjy4aGxiabQAhXL5YMKHVTNCPkQjRwIBw&url=http%3A%2F%2Fcookieteller.deviantart.com%2Fart%2FBilldip-520725279&psig=AFQjCNFJjhNVs4PXVe7MqPobRZ3Kt2r6-g&ust=1479138215492407
Disclaimer: Gravity Falls does not belong to me. The creator of the show is Alex Hirsh and the show Gravity Falls is owned by Disney XD. This is a fan-made story between the character Bill Cipher and Dipper Pines.