Suggestions by @Navy_Cove_Vale

John Travolta

as Old Man McGucket in Gravity Falls

Bruce Willis

as Old Man McGucket in Gravity Falls

J.K. Simmons

as Old Man McGucket in Gravity Falls

Skylar Gray

as Grenda in Gravity Falls

Txunamy Ortiz

as Candy Chiu in Gravity Falls

Richard Gere

as Stanford Pines in Gravity Falls

Jeff Goldblum

as Stanford Pines in Gravity Falls

George Clooney

as Stanford Pines in Gravity Falls

Harvey Guillén

as Soos Ramirez in Gravity Falls

Owen Rivera-Babbey

as Lil Gideon in Gravity Falls

Abby Glover

as Wendy Corduroy in Gravity Falls

John de Lancie

as Bill Cipher in Gravity Falls