Hazandra

The Hazandra was a gemstone owned by the Twelfth Doctor. It was one of four stones of it's type.

The Twelfth Doctor planned to use the stone as a power source for his "time distortion equaliser thingy". He gave the stone to a young Grant Gordon. However, believing the stone to be medicine for his cold, Grant ingested it and gained "superpowers" which helped form his alter-ego, the Ghost. (TV: The Return of Doctor Mysterio)

The Twelfth Doctor and Grant later went to search for the stone's siblings. (COMIC: Ghost Stories)