Happy Birthday, Dipper Pines (BillDip) [DISCONTINUED]

It's been four years since their last birthday in Gravity Falls, Oregon. Mabel is getting all the attention and Dipper feels left behind. What happens when Dipper leaves the party to greet an old "friend"?

Cover art credit goes to @KatzianXero on deviant art!
All characters are owned by the creator of Gravity Falls, Alex Hirsch! The story is mine, though.
This is BillDip! If you don't like it, don't read!
This will include the AU that Dipper is part demon, Alcor. I don't know much about this AU, so I'm just going off my own ideas!