The Weirdmageddon Apocalypse happens and Bill takes dipper as his pet. Dipper is 13 Bill is super old demon.

Fearamid

Bill is looking over his henchmaniacs partying and having fun then his head started tingling indicating someone was awake. Grinning Bill teleports into the top of the fearamid.

"Oh goody your awake Pinetree!" Bill said making the young woman jump in surprise on the normal mattress Bill her.

"Bill!" Dipper yelled angrily leaping toward the demon only to restrained by glowing blue chains.

"Tsk tsk." Bill says waving his finger making Dipper frown "You shouldn't attack your master Pet." He said smirking.

"Pet!" Dipper said in disbelief "I am no demon's pet you big stupid demon!" She growls.

"Well true you ain't 8-Ball, Amorphous Shape, Hectorgon, Keyhole, Kryptos, Paci-fire, Pyronica, Xanthar or Teeth's pet or any other demons pet but you are mine!" Bill chirped.

"What is this place anyway." Dipper said quietly arms crossed taking a seat on a couch.

"Oh this is the top of the fearamid! And that couch is made of human flesh!" Bill added making Dipper gasp quickly gating off the couch that was indeed sorta alive.

"Well that's really gross." Dipper muttered "And what makes you think I'm yours anyway?" She asked.

"Well that summoning tattoo on your back for one." Bill painted out lifting up her shirt making her squeak slapping his hand making him laugh "Ha! Hilarious! But seriously I only need to go half way." He said.

"Fine." Dipper reluctantly agreed letting him rile up her shirt and summoned a body mirror so she can so the giant black ink tattoo on her back "What when did this happen?" She demanded pulling her shirt down.

"When you were sleeping obviously." Bill said smugly then snapped his fingers changing Dipper's regular outfit.

"Hey!" Dipper snapped looking at herself in the mirror she's wearing a yellow dress, a black bow tied around her waist, no shoes and her hat was gone leaving a yellow and black bow "Great now I'm matching you." she said frowning at the look.

"That's not all!" Bill said snapping his fingers making his human body look 13 like Dipper "How do you like it?" His voice cracked a little making him blush as Dipper laughed "I'll only be in this form when I'm alone with you Pinetree." He said pulling her blue chains around her arms making her come forward.

"Uhh." Dipper says looking away not being used to being so close to boys her age...well that look like it anyway.

"Time to train you." Bill smiled wickedly making Dipper gulp already dreading what comes.