Armus

In 2364 Counsellor Troi was travelling back to the Enterprise-D in a shuttlecraft when it was pulled of course by a mysterious force which crash-landed it on Vagra II. Troi survived the crash, but when the Enterprise came to her rescue the ship was unable to beam her up due to a strange energy on the planet. The ship dispatched an Away Team, but on arrival the team was prevented from approaching the crashed shuttle by a strange being. The life form initially took the form of a viscous black liquid which lay on the surface. It blocked access by interposing itself between the Away Team and the shuttle, then assumed a slightly more Humanoid form. The creature communicated with the away team verbally, calling itself Armus. It refused all requests to allow the Away Team to help Troi, and when Lieutenant Yar attempted to walk past it Armus hit her with some form of energy discharge, killing her.

Armus demonstrated many powerful abilities. It seemed unaffected by phaser fire and was able to manipulate and even transport matter. Armus claimed that it had once been a part of beings not unlike Humans. In the distant past these beings had discovered a way to convert their negative personality traits into a physical skin, which they then shed. These people had subsequently become dazzlingly beautiful and had departed their home planet, leaving the 'evil' material - Armus - behind. Armus made several attempts to terrorize the Enterprise crew, but each time was frustrated by their total refusal to assist it. Eventually they realized that the energy field preventing transport was reduced in strength each time Armus was frustrated; Captain Picard beamed down and confronted Armus, provoking it into a rage of such magnitude that the ship was able to beam its crew back.

The Enterprise posted warnings to prevent any vessels from approaching Vagra II and abandoned Armus there. It's fate is unknown, but there is no reason to suppose that it is not still on the planet.