It had the ability to possess any living being by simply moving "into" them. This was in fact how it fed, and it required at least one life per month to survive. Only Force-sensitive beings skilled in the control aspect of the Force and having a strong will could escape being possessed and thus killed by the Black Mist.
When the Black Mist was "born" upon the Imperial research station, it proceeded to kill all beings aboard the craft, switching to a new body whenever its previous one was destroyed. Eventually, however, the crew of the ship sabotaged both its sublight drives and hyperdrive, trapping the Mist on the ship.
During this period with nowhere to go, the Mist learned to reprogram the ship's complement of R2 units and 3PO droids and armed them with blaster pistols and blaster rifles. It was not until the Sidewinder dropped out of hyperspace while on its way from Tegrat to Tatooine that the Mist had any hope of escaping. It immediately fired upon the ship with the research station's turbolasers, disabling the Sidewinders sublight drives, and brought the ship into the research station's hangar by means of its tractor beams. The group aboard the freighter boarded the research station to shut off the tractor beam holding them in place. The Black Mist lay in wait, allowing the group into the depths of the station, sending the occasional R2 or 3PO droid against them. Eventually the Mist appeared to the group in the body of the last crew member from the station. Though the group attempted to capture it, the moment they touched it, its corporeal body fell forward, and as its head struck the ground, it broke apart in a shower of dry, crusty fragments. The Mist immediately transferred into one of the group and ran back to the Sidewinder, hoping to repair its engines and escape. Unfortunately for its plan, the group managed to fire the research station's turbolasers at the Sidewinder, once again trapping the Black Mist but also stranding themselves.