It's been revealed at the Doctor Who panel at New York Comic Con, in addition to the Doctor and Matt Lucas character Nardole, the Christmas special, Return of Doctor Mysterio, also features Justin Chatwin Orphan Black as a literal superhero.
Here s the full image of Chatwin:
This Christmas, the Doctor joins forces with a superhero, played by @Justingchatwin, in…
The Return of Doctor Mysterio!
Steven Moffat said that his inspiration for the special was his obsession with superheroes, in particular Clark Kent.
Not Superman, but Clark Kent because Moffat loved the mild-mannered alter ego.