The Ux-Mal Entities are a large group of alien criminals from the Ux-Mal solar system who were exiled to the moon known as Mab-Bu VI during the 19th century. They were the main antagonists of the Star Trek: The Next Generation Fifth Season episode "Power Play." They were portrayed by Marina Sirtus (when they possessed Deanna Troi), Brent Spiner (when they possessed Data), and Colm Meaney (when they possessed Miles O'Biren).
Their consciousness were ripped from their bodies and left in the harsh storms as anionic energy to suffer an eternal Hellish sentence in this strange type of prison. They can possess any lifeform, biological or artificial (like androids). They tried to escape twice. The first time was via the ship and crew of the USS Essex in the 22nd Century, but due to the technological restrictions of the time, they could not escape. The second was the USS Enterprise NCC-1701-D. Jean-Luc Picard and his crew outwitted them in a daring calculated risk and forced them to return to the moon. It's assumed that Picard put a quarantine on the moon to prevent further encounters with the prisoners.