Suggestions by @markclaunch

J.K. Simmons

as Malleus in Once... The Book of Merlin

Olivia Munn

as Lighty in Once... The Book of Merlin

Milla Jovovich

as Pia in Once... The Book of Merlin

Jackie Earle Haley

as FlickBlade in Once... The Book of Merlin

Rami Malek

as Blu in Once... The Book of Merlin

Bill Skarsgård

as Shade in Once... The Book of Merlin

Eddie Redmayne

as Tint in Once... The Book of Merlin

Zendaya

as TriLilly Trilay in Once... The Book of Merlin

Ron Perlman

as King Leodegrance in Once... The Book of Merlin

Paul Giamatti

as Hops in Once... The Book of Merlin

Simon Pegg

as Crispin Quickheel in Once... The Book of Merlin

Tilda Swinton

as Lavina in Once... The Book of Merlin

Karl Urban

as Sir Gawain in Once... The Second Book of Arthur

Idris Elba

as Sir Bedivere in Once... The Second Book of Arthur

Tom Hiddleston

as Sir Tristian in Once... The Second Book of Arthur

Shawn Ashmore

as Sir Gaheris in Once... The Second Book of Arthur

Aaron Ashmore

as Sir Gareth in Once... The Second Book of Arthur

Idris Elba

as Sir in Once... The Second Book of Arthur

Laurence Fishburne

as Father Ector in Once... The Second Book of Arthur

Roman Griffin Davis

as Young Merlin in Once... The Second Book of Arthur