Deep in the marshes the Tree of Cognizance feeds on whatever living creatures come near it, using very powerful illusions and brute strength. It’s fruits are prized by those that understand the powers they offer.
Evil gives birth to many foul creatures, of these creatures the Negasek have emerged from a womb of darkness and terror. These powerful insect-like creatures radiate the dark force that gave birth to them, born of sheer negative energy, nearly dripping with the foulness of their diabolic nature.
A secret MLM (pyramid) company that offers eternal life, but in fact it transfers the life forces of its members to those position "above". If you get high enough, (meaning you get enough new members) you start to enjoy the benefits. Maybe a willing sacrifice is much more effective for the transfer. But no one says, that a suddenly unwilling member, threatening to tell the authorities, may not loose it involuntarily... thus start people to vanish, and aged corpses are deposited somewhere safe.