Mirror universe

As Sergeant John Benton once observed, a parallel universe was "some sort of mirror universe, like in that Star Trek episode where Spock had a beard". Amused, called Benton's assessment "succinct". (PROSE: The Face of the Enemy)

Behind the scenes

 * J. K. Woodward, who worked on the Star Trek crossover Assimilation², released pieces depicting counterparts of the Ninth Doctor, the Tenth Doctor and Eleventh Doctor in Star Trek's mirror universe.