Suggestions by @cw1234

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

Benedict Cumberbatch

as Ward in Gravity Falls: Dipper and Mabel Return

Michelle Fairley

as New Villains in Gravity Falls: Dipper and Mabel Return

Sarah Clarke

as New Villains in Gravity Falls: Dipper and Mabel Return

James Sie

as New Villains in Gravity Falls: Dipper and Mabel Return

Kristen Johnston

as New Villains in Gravity Falls: Dipper and Mabel Return

Elizabeth Banks

as New Villains in Gravity Falls: Dipper and Mabel Return

Lena Headey

as New Villains in Gravity Falls: Dipper and Mabel Return

Christopher McCulloch

as New Villains in Gravity Falls: Dipper and Mabel Return

Lance Henriksen

as New Villains in Gravity Falls: Dipper and Mabel Return

James Hong

as New Villains in Gravity Falls: Dipper and Mabel Return

John Noble

as New Villains in Gravity Falls: Dipper and Mabel Return