From the Back of the Book:
The Darkness Within
Nemeses of good, yet puppets of evil, the beleaguered men and woman who serve the Dark Powers may achieve their own terrible grandeur in the Dread Realms -- or they may somehow find their way back to the light. In any other world, they might be considered villains. In Ravenloft, they are champions.
Inside this book are rules for creating and developing anti-heroic characters, as well as prestige classes, information on the dark religions and secret societies in the Land of Mists and ideas for running campaigns.