The Key of the Scion looks much like the Key of the Caretaker, but the eyes of the skull on the top of the pole are green. Unlike the other key however, it is a real key that can open doors in the Catacombs. It is also used to send the dead to Lithos.
The Avatar received the Key of the Scion from Vividos in Ultima VIII, after meeting Lithos in the Hall of the Mountain King. Using it to send Lothian to Lithos, The Avatar needed it to gain access to more areas of Morgaelin.