Bill is a shape shifter causing mayhem through the lands. Dipper is 18 Bill is super old demon.

Forest of mysteries 1800s

"Be careful Dipper this land hasn't been recorded in books yet." Ford warned leading a trail for his niece.

"And why is that?" Dipper said struggling to get a branch off her pink dress.

"Those who do disappear. Some say it's a witch others say bear attacks." Ford said.

"Most likely wild animals are in here since it is the forest after all." Dipper said matter of factly.

"Now Dipper what have I said about keeping an open mind?" Ford scolded her but nothing "Dipper?" He said and looked around.

In a nearby hole

"Uh my head." Dipper groaned holding her head from falling down the hole.

"Pinetree?~" something whispered making Dipper jump.

"Uh who's there... I have an axe and I'm not afraid to use it!" Dipper warned holding up her axe.

"Cute!" The creature said stepping out of the shadows of the giant tunnel hole revealed a deer?

"A deer has been reeking havoc in our town?" Dipper said in disbelief.

"Nope!" it chirped morphing into a wolf, a bear, a lion, some kinda alien and then a handsome well dresses man "Names Bill Cipher." He introduced.

"Your a witch!" Dipper screeched trying to run but Bill grew tentacles to scoop up the girl.

"You know witches are girls right? I would be a warlock." Bill informed.

"Help warlock!" Dipper screamed but Bill shushed her with a hand then pulled away.

"Did you... Lick my hand?" Bill asked surprised then laughed "I like you kid!" He said.

"Put me down warlock!" Dipper says while struggling in the monster's hold.

"Warlock more like shape shifter kid it's in my DNA!" Bill said shifting into multiple forms.

"Dipper!" Ford yelled from the hole Dipper fell from "I'm coming for you!" He said.

"Welp looks like funs over kid but I'll be watching you!" Bill says letting Dipper down then kissed her lips.

"Uh what why..." Dipper gasped blushing while Bill roaming in the shadows watching her be rescued then follow her home.