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.
The party is walking through the forest at night when they come upon a clearing. Half a dozen black-robed corpses lie scattered across the ground, and a pentagram of blood is shoddily drawn in the dirt.
It seems these people summoned something they could not control. Whether or not the demon returns is up to the GM, but it would be just as rich if the demon never returned, and for the rest of the night, every stray sound or odd shadow will be jumped at!