Tales of Tolgard
Ghost dragons are an incorporeal form of undead dragon. They are most often created when a powerful dragon is killed and its hoard looted. In such a case, this being can only be laid to rest by returning its treasure, or one of equivalent value, to its lair. If this occurs, the ghost dragon will settle on its hoard and dissipate, taking its hoard with it into the afterlife.
Ghost dragons retain most of their abilities that they had in life with a few exceptions and additions. They retain whatever breath weapon they had in life and gain a second one. This new breath weapon is a cone shaped cloud of gray mist that ages anyone it touches. They are also extremely difficult to destroy through violence; even if one is forced to dissipate through violence, and not the above mentioned way, it will return in no more than a week, sometimes less.