A Deal's a Deal (Gravity Falls)

Dipper and Mabel Pines have returned to Gravity Falls for their summer break. This time, though, they meet a new friend...
Not only that, but an old enemy has returned, now seeking revenge on the Pines family.
Can Mabel, Dipper, and their new friend defeat him?
But little do they know, is that Bill isn't working alone.

Still horrible at descriptions so please don't mind it. I'll probably rewrite it when I have time.
Gravity Falls belongs to Alex Hirsch
Cover done by me