Mara

You come into possession of a very old looking blank notebook, old yet in pristine condition. The foreword in the notebook invites you to unload your darkest thoughts and fantasies into this Book of Vengeance, to write out terrible punishments for everyone you feel has wronged you, somehow. What you do not realize, is that Mara, a powerful demon, is bound to the book by a curse from Lucifer, and is compelled to actually carry out all the evil thoughts you may list there.