It's Only the Beginning (A Gravity Falls Fanfic)

Trisha's summer plans are ruined when her parents told her that she'll go into a sleepy town named Gravity Falls, Oregon and bond with her mother's friend, Stanford Pines. She has nothing to do there, as she considers that the town is boring. She meets Mabel, Dipper and Stanford Pines, Soos and a pig named Waddles. Trisha finds herself falling deeper and deeper into the mysteries of Gravity Falls. Everything goes wrong when a mind demon, named Bill Cipher, steals something precious and attacks them and summons different kinds of creatures and traps to kill them. Can they
solve the mysteries of Gravity Falls and defeat Bill? When there's still time?

I surely don't own Gravity Falls.
And the characters except for my oc.
There might be a slight Dipper x OC
But will not be shown commonly.