A Star Trek episode so iconic that it has entered into common usage. Everyone knows that your evil universe counterpart [has a beard](http://tvtropes.org/pmwiki/pmwiki.php/Main/BeardOfEvil).
Again, the episode gives Kirk a chance for some good acting, with his brief appearance as the mirror universe Kirk. There’s also an opportunity for a lot of interesting work from the secondary characters such as Chekov or Sulu.
Overall I’d say this is one of the two or three best episodes that I’ve seen so far.
Great trek moment: The mirror universe, with its inevitable counterpart, the evil universe beard. It would also seem from the costumes that short skirts = good, midriff tops = evil.
(It takes a pretty special episode to push Spock mind melding with McCoy off the list…)
There’s also, I think, an appearance of something looking a lot like a replicator. This is the second time (there was one in Tomorrow is Yesterday as well). Not sure if it’s a replicator or not.
33 down, 704 to go.