Within a kingdom the prince or princess has died or been killed and the Queen has been driven half-insane with grief.What if one of the PC's was mistaken for the dead prince or princess and not allowed to leave? There would be advantages in accepting the role, but would it be worth it?
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.