Star Trek's Mirror Universe Explained

In TOS' "Mirror, Mirror," Prime Kirk discovers his Mirror counterpart has been secretly using a device called the Tantalus Field. With it, Mirror Kirk can monitor anyone on his ship and, should he choose, disintegrate them with the touch of a button. His concubine, Marlena, says it's how he became captain, implying he used it to murder his predecessor. But according to the "Before Her Time" documentary on the season 4 Enterprise Blu-ray, there was almost a reveal that the device did something else entirely. 

According to the documentary, rather than the two-parter which ultimately became "In a Mirror, Darkly," the Enterprise creators wanted William Shatner to reprise his role as the Mirror Kirk, aka Tiberius. In "Mirror, Mirror," it's said Tiberius got the Tantalus Field from an alien scientist's "plundered lab." The proposed Enterprise story would reveal that rather than killing, the device actually sends its victims to a penal colony in the Prime Universe. Tiberius would find himself at this prison, presumably surrounded by a bunch of people he sent there, such as his predecessor, who would likely have been the Mirror Captain Pike. 

Unfortunately, negotiations between Shatner and Paramount didn't work out. However, it's fun to consider the idea of Shatner reprising the role, particularly when you consider how little we see of Tiberius in "Mirror, Mirror."