Welcome Home.

Contains spoilers, if you haven't seen the entire show.

Several years after the events of the show.
Dipper and Mabel return to Gravity falls,both now 17, for a summer reunion with their friends and Gruncles. However the morning after they arrive a strange boy with golden hair appears on the doorstep of the mystery shack, with no memory of who he is or where he came from. The only thing he seems to remember is his name. Bill Cipher.
(Triggers for mentions of suicide, self harm, depression, anxiety, past trauma and past abuse.)