Harry Potter/Sherlock Holmes

Sherlock Holmes (Robert Downey Jr) as Harry Potter

John Watson (Jude Law) as Ron Weasley

Mary Morstan (Kelly Reilly) as Hermione Granger

Mycroft Holmes (Stephen Fry) as Albus Dumbledore

Lord Blackwood (Mark Strong) as Severus Snape

Professor Moriarty (Jared Harris) as Lord Voldemort