The Legions were a race of beings who possed a threat because of their misuse of temporal powers. They existed in seven dimensions.
Biology
Because of their dimensional composition, Legions appear to Humans as a group of disconnected shapes and they move in and out of the usual three: a three-dimensional cross-section of a seven-dimensional object. Because of this state, their voices change pitch erratically. They can also drift around in Time if they aren't concentrating. If they reappear in the main three dimensions within another being, they rip that being apart. (NA: Lucifer Rising)
Technology
The Crystal Bucephalus restaurant used technology similar to that of a TARDIS, which was directed by a Legion Tank. (MA: The Crystal Bucephalus) IMC's quantum collapsers were also harnessed from the Legions. (MA: Lucifer Rising)
History
Species that the Legions had encountered include the Cimliss, the Usurians, and the Okk. (MA: Lucifer Rising)
The Time Lords developed a standard sentence of 150,000 years imprisonment for races that misued their temporal powers on the scale that the Legions did. (MA: The Crystal Bucephalus)
In 2157, the Legion aided IMC in taking over Lucifer. (NA: Lucifer Rising)
- "Lucifer Rising" refers to "Legion" as an individual whereas "The Crystal Bucephalus" states Legion is a species. This might be explained if the Legions were a hive mind, implying there were all one being.