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The Best Mirror Universe Episodes in the Star Trek Series

If there's one thing the Star Trek franchise is well known for, it's the parallel universe that has existed since the Original Series broadcast an episode called "Mirror, Mirror" back in 1967. That episode established the existence of a Mirror Universe, which consists of a reality in which Starfleet never rose, but was replaced by the Terran Empire. Over the course of the numerous series set within the Star Trek universe, that Mirror Universe has been explored, which means it has a history as rich and long as that of the Prime Universe.

Almost every series has delved into the Mirror Universe at one time or another, but not every episode from that alternate reality is necessarily the best. Depending on who is in the episode, what happens, and how it relates to what's going on in that series' normal continuity says a lot about what makes those episodes work. We don't have a magic mirror to tell us which episodes are the best, and that's where you come in. Take a moment to look through the list and vote up your absolute favorite. Was it the first one ever made, or a more recent foray into the parallel universe as seen on Star Trek: Discovery? Only your votes can decide, so vote up the best Mirror Universe episodes below!

  • In the episode that started it all, four of the crewmembers from the USS Enterprise switch places with their counterparts in the mirror universe. In order to survive, they must avoid being discovered for who they are as they make their way back to their own universe while avoiding tipping off the crew of the mirror Enterprise.

    • Original Airing: Oct 06 1967
    • Season: Star Trek: The Original Series Season 2
    • Episode Number: 4
    • Series: Star Trek: The Original Series
    Is this a good trip to the other side?
  • 2

    In a Mirror, Darkly (2)

    The second part of the two-part episode follows the destruction of the Enterprise with the crew retreating to the Defiant, which the Mirror Archer sets his sights on to try and take over the Terran Empire, but it is the Mirror Hoshi Sato who ultimately gains the upper hand and replaces him as the Empress of the Terran Empire.

    • Original Airing: Apr 29 2005
    • Season: Star Trek: Enterprise Season 4
    • Episode Number: 19
    • Series: Star Trek: Enterprise
    Is this a good trip to the other side?
  • When the crew of the ISS Enterprise finds the USS Defiant, they learn that it is a vessel from 100 years in the future. It had last been seen in the franchise in "The Tholian Web" from the original series, but it found a way through both universes via a rip in space.

    • Original Airing: Apr 22 2005
    • Season: Star Trek: Enterprise Season 4
    • Episode Number: 94
    Is this a good trip to the other side?
  • More than a century after the events of "Mirror, Mirror" from the original Star Trek episode, Doctor Bashir and Major Kira find themselves in the same place. They arrive in a Mirror Universe where the Terran Empire has been replaced by an Alliance of Klingons, Cardassians, and Bajorans who use the human race as slave labor across the galaxy.

    • Original Airing: May 15 1994
    • Season: Star Trek: Deep Space Nine - Season 2
    • Episode Number: 23
    Is this a good trip to the other side?