The Book of Vile Darkness
'The Book of Vile Darkness is originally said to have been penned by the archmage (and then, lich), Vecna.
Legend also has it that this heavy tome, bound in the skin of various humans and fiends, contains the totality of Vecna's knowledge of the Lower Planes. Inside are notes and rituals for researching, binding and destroying all types of Fiends.
Unfortunately the book itself is cursed, containing a portion of the evil that lurked within Vecna's tainted soul, and can only be briefly used by mortals. The archmage, Iggwilv is the only known mortal to have survived a complete reading and, even then, she had to transcribe much of the knowledge out of this and into her 7-volume work the Demonomicon in order to use it with certainty.
Occasionally books that report to be "copies" of this work turn up. None are complete of course and few really give much insight into fiends. It is rumoured that the original is still out there, somewhere, waiting for the time at which Vecna returns to claim dominion upon Oberon.
