Adventures in the Quivering Forest
Lumber is infected with splinterwaifs because of the unique properties of the Quivering Forest.
Follow the cursed timber to a logging camp in the Quivering Forest.
Discover Wingclipper, the evil ranger who hunts fey (and who is being influenced by Treerazer).
Discover the incubus who prefers worg form and is a pawn of Graz'zt.
Secret of the Standing Stones
Treerazer from Paizo.
Dungeon 25 - The Standing Stones of Sundown.
The real reason for the Quivering Forest: it's an early warning system should Treerazer be released.
Ten shamans and druids of the human civilisation that built the Citadel of the Raven performed a ritual to bind Treerazer into a standing stone, at the cost of their own petrification into ten standing stones. Treerazer had been menacing the elves and the humans rescued them.
Treerazer has been freed and is gathering power.
To be freed, the fey and primal protectors first had to be defeated. I think this was due to infiltration by Tyralandi, the half-incubus nymph thrall of Graz'zt.