Arquess

The Arquess, the Smoke of Mysteries and Deceit, as named by the Vigilant eremites of Andurax, was a gemstone. As of 1992, only four such stones remained in the universe.

Its powers were used by Ethan Hall to alter his body and become the Smoke. With the help of Grant, he realised the trouble he caused with those powers, he decided to give the gemstone to the Twelfth Doctor. (COMIC: Ghost Stories)