Mythos

From the Legend of the Old Ones:

"Some people found ancient writings and ruins from beneath seas, and found out that The Great Old Ones can still be contacted with certain spells. The knowledge of such things, called the Cthulhu Mythos, was such a horrifying thing that it drove most people insane, or to commit suicide."

The cultist draws her powers from the Mythos. When she has studied them enough, Master Chthughan will teach her some more of it, and she will gain a Mythos Level.