Suggestions by @markclaunch

Lily James

as Glenna in Once... The Book of Merlin

Score: 0

Tilda Swinton

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

Score: +1

Sean Bean

as King Uther Pendragon in Once... The First Book of Arthur

Score: +1

Lena Olin

as Queen Igraine in Once... The First Book of Arthur

Score: +1

Liam Neeson

as King Gorlois in Once... The First Book of Arthur

Score: +1

Laurence Fishburne

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

Score: +1

Amanda Seyfried

as Princess Elaine in Once... The Book of Merlin

Score: +1

Maisie Williams

as Sister Elenne in Once... The Book of Merlin

Score: +1

Joan Cusack

as Morgausa in Once... The Book of Merlin

Score: +1

Ian McShane

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

Score: +1

Anya Taylor-Joy

as Nimue in Once... The Book of Mordred

Score: +1

Anya Taylor-Joy

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

Score: +1

David Tennant

as Merlin in Once... The Book of Merlin

Score: +1

Angelina Jolie

as Vivian in Once... The Book of Merlin

Score: +1

Natalie Dormer

as Morgause in Once... The Book of Merlin

Score: +1

Roman Griffin Davis

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

Score: +1

Zoe Saldaña

as Princess Isolde in Once... The Book of Merlin

Score: +1

Helena Bonham Carter

as Queen Jezzel in Once... The Book of Merlin

Score: +1

Christopher Eccleston

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

Score: +2

Forest Whitaker

as The Shaman Dagara in Once... The First Book of Arthur

Score: +1