Suggestions by @deerzelwashington

Chris Eubank

as Speed Force in Flash 2

Score: -1

Holland Roden

as Iris west in Flash 2

Score: +1

Jamie Campbell Bower

as Voice in Flash 2

Score: +1

Teddy Sears

as Black flash in Flash 2

Score: +1

Zane Phillips

as The Flash in Flash 2

Score: +1

Tom Ellis

as Shade in Zatanna

Score: -1

Camila Mendes

as Eternal Knight in Zatanna

Score: +1

Dan Stevens

as Jason blood in Zatanna

Score: +1

Peter Capaldi

as Dr Fate in Zatanna

Score: +1

Steve Howey

as Etrigan in Zatanna

Score: -1

Bill Burr

as Etrigan in Zatanna

Score: -1

Danielle Rose Russell

as Zatanna in Zatanna

Score: 0

Crystal Reed

as Wonder Woman in Zatanna

Score: +1

Camila Mendes

as Zatanna in Zatanna

Score: -2

Rob Mac

as Deadman in Zatanna

Score: +1

Finn Wolfhard

as Klarion in Zatanna

Score: -1

Zach Roerig

as The Flash in The JSA

Score: +1

Peter Capaldi

as Kent Nelson in The JSA

Score: +1

Morgan Freeman

as Dr Fate in The JSA

Score: +1

Milly Rosso

as Star girl in The JSA

Score: +1