Suggestions by @cw1234

Michael Dorn

as Guest Voices in Gravity Falls: Dipper and Mabel Return

Michael Chiklis

as Ward in Gravity Falls: Dipper and Mabel Return

Michael Kelly

as Ward in Gravity Falls: Dipper and Mabel Return

Aidan Gillen

as Ward in Gravity Falls: Dipper and Mabel Return

Roger Cross

as Guest Voices in Gravity Falls: Dipper and Mabel Return

Brad Breeck

as Composer in Gravity Falls: Dipper and Mabel Return

Tim mckeon and Alex Hirsch

as Writer in Gravity Falls: Dipper and Mabel Return

Alex Hirsch

as Director in Gravity Falls: Dipper and Mabel Return

Tom Vaughan-Lawlor

as New Villains in Gravity Falls: Dipper and Mabel Return

Dee Bradley Baker

as Waddles in Gravity Falls: Dipper and Mabel Return

Felicia Day

as Guest Voices in Gravity Falls: Dipper and Mabel Return

Rhys Darby

as Guest Voices in Gravity Falls: Dipper and Mabel Return

James Cromwell

as Guest Voices in Gravity Falls: Dipper and Mabel Return

Haley Joel Osment

as Guest Voices in Gravity Falls: Dipper and Mabel Return

Bruce Harwood

as Mr Pines in Gravity Falls: Dipper and Mabel Return

Tricia Helfer

as New Villains in Gravity Falls: Dipper and Mabel Return

Peter Weller

as Ward in Gravity Falls: Dipper and Mabel Return

Zachary Quinto

as New Villains in Gravity Falls: Dipper and Mabel Return

Glenn Morshower

as Ward in Gravity Falls: Dipper and Mabel Return

Mark Strong

as Ward in Gravity Falls: Dipper and Mabel Return