The Diary of young girl who finds herself trapped in purgatory, searching salvation and trying to make sense of that which is deliberatly insane. (A prelude to the entry found in my Chasers submission.)
Ideally the creatures described within this (ongoing) sub will be detailed in turn as their own seperate submissions eventally painting a complete picture of purgatoy.
If you want to add a "supernatural" touch to your campaign, define the rules of magic and the universe. Make your players comfortable with those rules. Then your new supernatural creatures must then break those rules.