The last eight episodes primarily focus on the gang trying to stop Bill Cipher, a dream demon with infinite power who wants to take over the world with weirdness, with J. K. Simmons joining the main cast as Ford Pines.

[6] The main characters, voiced by Jason Ritter as Dipper, and Kristen Schaal as Mabel, with series creator Alex Hirsch portraying Grunkle Stan and Soos, and Wendy Corduroy played by Linda Cardellini, reprise their roles.

The recurring characters comprises the voices of Dee Bradley Baker as Mabel's pet pig, Waddles, and Hirsch also playing Old Man McGucket, the "local kook" of the town.

Kevin Michael Richardson plays Sheriff Blubs, with partner Deputy Durland being voiced by Keith Ferguson.

Voice acting veteran John DiMaggio plays Manly Dan, a strong lumberjack and father of Wendy.

Toby Determined, a journalist for Gravity Falls' Gossiper, is voiced by Gregg Turkington, and Will Forte plays Tyler Cutebiker.

[10] Stan continues to work on the portal while the Mystery Shack throws a grand re-opening party after the Li'l Gideon incident.

Guest star: Neil deGrasse Tyson as "smart" Waddles When Dipper, Mabel, Soos, and Wendy confront Old Man McGucket about his connection to the author of the journals, they discover a secret society in Gravity Falls that erases people's memories of the supernatural.

Guest star: Peter Serafinowicz as Blind Ivan Blendin challenges Dipper and Mabel to a futuristic, deadly battle for revenge of his past humiliation.

After government agents take Stan into custody, Dipper and Mabel begin to question how much they really know about their Grunkle and must work out whether or not they truly trust him anymore.

Mabel and her friends go on a magical quest to get unicorn hair in order to protect the Mystery Shack from Bill Cipher.

"Weirdmageddon Part 1"[note 4] – Bill Cipher has been freed, and unleashes an apocalypse upon Gravity Falls as his minions run rampant through the town.

as The Horrifyingly Sweaty One-Armed Monstrosity,[note 5] Danielle Fishel as Pyronica, Patrick McHale as Hectorgon, Andy Merrill as Teeth, Brian Bloom as Rumble McSkirmish, Nathan Fillion as Preston Northwest, Justin Roiland as Blendin Blandin, and Dave Wittenberg as Time Baby and Lolph "Weirdmageddon 2: Escape from Reality" – Dipper, Soos, and Wendy enter Mabel's bubble to rescue her, only to discover it is her own personal paradise.