Mirror Cat
The Mirror Universe was a parallel reality accessed by the Dwarfers. ("Only the Good...")
Antivirus[]
When Red Dwarf was being slowly consumed by a corrosive virus, Kochanski suggested travelling into a mirror universe. There everything would be opposite and a viable antivirus would exist.
Kryten quickly created a prism laser that was fired at a mirror in Captain Hollister's quarters. This created a gateway to a mirror universe which Rimmer stepped through before the laser failed, needing to be repaired.
Opposites Attract[]
Rimmer found that in this universe, he was the ship's commanding officer. He reveled in this role, humiliating the mirror version of Frank Hollister who was a lowly errand boy. He was also delighted by what he found when he looked under his bedclothes. The woman he assumed to be his lover turned out to be a nun.
Mirror Kochanski
As he went in search of a scientist to develop an antivirus, he made his way to the laboratories. Here he met the Mirror Kochanski, a surly and ignorant secretary. She insisted that he would need The Professor. He turned out to be an alternate Cat, who was indeed an opposite, being incredibly well-educated and insightful. He quickly analysed the viral specimen that Rimmer had brought and identified the antivirus as an alkali called Cesiumfranciolithicmyxialobidiumrixydixydoxidrexidroxhide. He wrote it down on a long piece of paper for Rimmer.
When Rimmer returned through the repaired mirror, he discovered that the virus had spread all over the ship and that the cure he had brought had turned back into the virus. He tried to follow his crewmates back into the mirror universe, but the prism laser had corroded beyond repair. ("Only the Good...")
Deleted scenes[]
Mirror Lister
There were several scenes set in the mirror universe that had to be cut from the finished show. These included Craig Charles as an upper class officer version of Lister, Robert Llewellyn as a slovenly cleaner, and Chloë Annett as a silly, giggly airhead secretary. An extended version of her scene showed her explaining to Rimmer that she did not need to work as a secretary, since she was qualified to work in a cake shop. (Series 8 DVD)