The Black Book

In his search for ultimate knowledge did not the sorcerer Tellaborabi sign his name in the Black Book of Azathoth? And later, when his frightened acolytes broke down the door to his sanctum they found not an all knowing sage but instead a drooling madman who had clawed out his own eyes.

(from the confessions of Psylacheus the Heretic)

Revenant from the Bog

Those sorcerers of old Hyperborea would cast the bones of a man into a swamp and command elementals to inhabit them. In time those bones would rise covered in the substance of the bog, a shape vaguely like a man but a thing of horror and an affront to the spirits of the earth .
(from the Scrolls of Vecra Tutthoon)