According to official rules of the International Astronomical Union (IAU) — the governing body that assigns official scientific monikers to planets and other solar system bodies — land features on Charon will be named after "destinations and milestones of fictional space and other exploration," among other things.Tolkien and Lovecraft have been drawn on, but so has Mandaean mythology:
FFeatures on Pluto itself, however, will earn monikers from the underworld, picked from among the world’s mythologies, including gods, goddesses and dwarfs associated with the underworld.
In addition, another land feature is known as Krun, named after an overlord of the Underworld in the Mandaean faith. According to the Our Pluto website, which was the venue for public voting on Pluto names, the Mandaeans are "the last surviving Gnostic group from late antiquity."Some past posts on Mandaean and the Mandaeans are here, here, and here, and links.
UPDATE (28 July): James McGrath, expert in all things Mandaean, has additional information here.