Cult Of Mithras

A Cult of Mithras is a damnable thing to fight, for it exists not in flesh and blood but in the hearts and minds of the people it effectively possesses. It is, essentially, a Gestalt consioscness created by the collective thoughts of a group of inter-related people. Most often taking shape in isolated communities, ideally countryside towns and ghettoes, it forms in the collective psyche of the people until it builds up enough power to actively influence their thought patterns.
Often dubbed the "Synagogue of Satan" by many Adepts, the Mithriac Cult has existed for as long as anyone can remember, in some place and in some form. The Cult is difficult to fight because most of its members are ordinary people whose thoughts are being heavily influenced by the Gestalt entity. They usually don't realize just what it is they are doing.
Of course the worst followers of a Mithriac Cult are those who come to realize there is a Gestalt... and knowingly embrace it. These persons, often gossipers and social mongers, will actively work against anyone who threatens the Cult, even putting themselves at great risk in the process. 
Most members of the Cult do not realize they are being controlled. Usually the influence exerted by the Gestalt is merely self-preservation: people are keenly aware of public opinion and expectations and are afraid to be branded an outsider or weird in any way, this sets the stage for full Gestalt control as the people subvert their own wills over to the group mind. Eventually, they begin to think in certain ways just because they believe it is expected of them. 
Once the Gestalt Consciouscness has gained enough influence, it can control their emotions, causing them to act in ways they never would otherwise. Adepts have found themselves attacked by mobs of townspeople intent on killing them, despite the fact the townspeople, afterwards, could think of no reason why they would want the Adepts dead? Theft, assassination, even suicide in some cases have been linked to a Mithriac Gestalt mind.
And what really makes a Cult of Mithras frightening? Adepts themselves are not immune to it. There are recorded cases of Adepts becoming 'infected' with a Gestalt influence, usually from growing up or living for a time in a community harboring one. 
This doesn't mean a Gestalt can just take somebody over in a flash, there has to be a prolonged period of living under the Cult's influence. Also, it can only affect people who have subverted their wills over to the hive mind. Strong-willed individuals or people who retain their own opinions are immune to the Cult's powers.
The only way to destroy a Cult of Mithras is to either reveal the Gestalt's presence in the minds of the people or eliminate the inner-circle of followers who are actively pushing for the Gestalt mind. In this the Assassin and Philosopher Adepts have proven invaluable, able to both 'see' the invisible Gestalt entity at work in the townspeople as well as the ability to remove its key personnel (they need not be killed, by the way, merely removed from the community and taken far away were their connection to the Cult cannot be maintained). 
The Cult takes its name because most Gestalt minds, once they are fully developed, will actually communicate with Adepts through the minds of their puppets. They refer to themselves as 'Mithras' and appear to have some history with the prehistoric mystery cult of the far east. Some Adepts have speculated that Mithras may have been the name of a real person or cult who started the first Gestalt mind, and the memory of that cult has been passed down through history in the minds of human beings. Every time a new Gestalt arises, it believes itself to be a reincarnated version of the first 'Mithras.'