The parasite was able to drain energy from, as well as duplicate, machinery and living matter.
The lifeform appeared like groups of floating protein molecule chains. A large central core of these protein chains resided within a volcano. It was able to send smaller sections of itself out to hunt for and drain energy, then return it to the main body. It was theorized that the lifeform hibernated to conserve energy and was capable of producing evidence of movement in order to lure passing energy sources to the surface. Positive ions, such as those powering a shuttlecraft, seemed particularly tasty. Negative ions were able to repel and weaken it.
The parasite apparently subsisted on energy from magma in the volcano, or else it could not exist on a barren asteroid. Expelled lava in the crater and in the lava flow miraculously cooled in moments, for example, as if all its heat were being leached away. The lifeform may be able to adjust the temperature of areas of the magma to trigger volcanic eruptions. Its actions seemed based on instinct, driven by hunger, and therefore might not be sentient.
At some point in the past, the asteroid it lived on passed through a star system. The lifeform was able to lure an interplanetary, chemically-powered spacecraft to the surface and kill its humanoid crew.
In the year 2267, it detected the passing of the USS Enterprise and produced signs of movement to lure a landing party to the surface. The Tactisian was able to create fully-functional mechanical duplicates of the Galileo shuttlecraft, a video camera robot, and convincing duplicates of James T. Kirk, Calder, two security officers, Montgomery Scott and Leonard McCoy. It had trouble duplicating the biology of Spock. (TOS comic: "The Mimicking Menace")