Van Richten's Guide to Fiends (Advanced Dungeons & Dragons : Ravenloft, No 9477)

Dr. Van Richten exposes the nature, origin, stengths and weaknesses of the Fiend, and how it reaches the Land of the Mists. He explores the character of these beings, and their connections to the people and the Land itself. In the ultimate irony, these awesome creatures are as trapped by the Land as any mortal, seduced by prospects of power and glory!