Suggestions by @bradleysigma

Diana Rigg

as Mrs. Peacock in Clue

Nathan Fillion

as Colonel Mustard in Clue

David Mitchell

as Professor Plum in Clue

Adam Scott

as Mr. Green in Clue

Rowan Atkinson

as The Bursar in Discworld

Stephen Fry

as The Dean in Discworld

Hugh Laurie

as Mustrum Ridcully in Discworld

Jonathan Banks

as "Mac" McAnally in The Dresden Files

Fran Kranz

as Hades in The Dresden Files

Jonathan Pryce

as Father Forthill in The Dresden Files

Gwendoline Christie

as Sigrun in The Dresden Files

Sean Maher

as Mortimer Lindquist in The Dresden Files

Enrico Colantoni

as Uriel in The Dresden Files

Evanna Lynch

as Murphy in The Dresden Files

Crispin Glover

as Nicodemus in The Dresden Files

Zach Woods

as Binder in The Dresden Files

Iain Glen

as Michael Carpenter in The Dresden Files

Jerome Flynn

as Jared Kincaid in The Dresden Files

Anna Kendrick

as Sarissa in The Dresden Files

Iwan Rheon

as Lloyd Slate in The Dresden Files