None of us lived during the 18th century (or whenever the game is set - we haven't decided the details yet). Although fascinated by the folklore of the time, we don't know enough to craft a realistic period piece.
Well, the only way to get up to speed on the weird and wonderful beliefs of our ancestors is to study them.
I heard about some very interesting books by a Norwegian folklorist named Ørnulf Hodne. His book "Norsk Folketro", roughly translated to "Norwegian Folklore", seemed like the perfect way for a basic crash course.