Suggestions by @rafaellain

Mark Strong

as Severus Snape in Harry Potter

Score: -1

Cillian Murphy

as Lord Voldemort in Harry Potter

Score: +2

Emma Thompson

as Minerva McGonagall in Harry Potter

Score: 0

Andy Serkis

as Alastor Mad-Eye Moody in Harry Potter

Score: +2

Jared Harris

as Alastor Mad-Eye Moody in Harry Potter

Score: +2

Jared Harris

as Albus Dumbledore in Harry Potter

Score: +3

Pierce Brosnan

as Albus Dumbledore in Harry Potter

Score: +3

Richard E. Grant

as Albus Dumbledore in Harry Potter

Score: 0

Stephen Fry

as Rubeus Hagrid in The PERFECT Harry Potter Reboot

Score: +2