I find many of the evil organizations in rpgs to be one-dimensional and cliche, so I tried to write a couple that were a little more complicated.
These religious devotees wear shrouds stolen from corpses and rub their bodies with cremation ash. They hold that good and evil are really the same thing. Indeed, they believe that all things are one.
By ritually embracing pollution in the form of cannibalism, they are revealing the illusory nature of the social taboos against it and, by extension, all other taboos and moral categorizations. They seek power and, when they obtain it, seek to find even more power, because they believe that the accumulation of enough power will allow them to escape birth and rebirth on the outer planes as petitioners.
The order does not fear the afterlife because they believe that, since all things are one, the various lower planes and upper planes are really the same place, and torment is the same as pleasure.
The Cult of Great Worm
A religion that venerates a temporal deity, these cultists cultivate mulberry forests and wear ceremonial garbs of the finest silk. Their deity is a vast, nearly immobile, man-devouring worm that the cult believes will pupate into a great deity once it has been fed enough.
Eons ago a great deity -the cultists would say the greatest deity- perished, and Great Worm spawned in the rotting, divine cadaver. Back then, it was as small as a man. Immortal and invulnerable, it remained until men were created, and fed upon them. Eventually, it grew too large to hunt for itself, but did not starve to death nor diminish in size.
Centuries later, a tribe of men began to worship it and draw power from it, despite its apparent lack of intelligence or acknowledgement of this worship. In gratitude for these gifts, the tribe would feed its enemies to Great Worm, who would not eat any food save the flesh of men. This tribe was the ancestor of the current-day order.
Great Worm is now so large that his slightest movement causes tremors in the earth, and still he has not spun a cocoon, nor pupated. He resides amidst a vast mulberry forest, his maw opening and closing, dripping filthy poison. One of these days, the cult maintains, he will finally be sated, and spin a vast cocoon of fine silk. What will emerge from that cocoon, nobody can say.