In the year 2364, a shuttlecraft from the USS Enterprise-D crash-landed on Vagra II. The Enterprise sent down personnel to conduct a rescue, but the away team was stopped by Armus, who had surrounded the shuttle with an impenetrable force field. As the away team tried to reason with Armus, it simply mocked them and toyed with them for its own amusement. It enveloped Cmdr. Riker within its liquid form (though released him a short while after) and it attacked Lt. Tasha Yar with some form of psychokinetic charge that killed her instantly.
The Enterprise crew were only able to rescue the shuttle crew when Captain Picard kept Armus distracted as the two talked about the possibility of Armus leaving Vagra II to find the race that had abandoned it. With Armus suitably distracted, his energy barrier dwindled and the Enterprise was able to beam out the shuttle occupants as well as Picard. Armus was left alone once more and the Enterprise fired a photon torpedo upon the shuttlecraft to make sure Armus couldn't leave the planet. Warning beacons were then placed around Vagra II to ensure that no other ships would fall prey to Armus.
- Liquid-shifting - Armus' natural form is that of a pool of black ooze. He can mold himself around objects or take on a vaguely humanoid shape.
- Immortality - Armus has no definite lifespan and is immune to phasers and other such weapons. He seems to feed off energy.
- Psychokinesis - Armus can project invisible fields of energy to block people's movements and can even kill enemies instantly.