Tactis II was rogue asteroid located somewhere in the galaxy's Alpha or Beta Quadrant.
History and specifics[]
Tactis II had a barren surface dominated by an active volcano. A parasitic non-humanoid entity living within the volcano was capable of duplicating humans, robots and even their shuttlecraft.
In 2267, the USS Enterprise investigated the asteroid to make sure it didn't pose a hazard to Federation planets. Lieutenant Calder accompanied a shuttle landing party that encountered the Tactisian entity. (TOS comic: "The Mimicking Menace")