“ 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.”
“ There exists a prestigious academy with a history going back hundreds of years. Graduates are highly skilled and very much sought after for employment. For purely traditional reasons, the academy requires its students to become proficient in a skill or area of knowledge that has no use in the modern world. This could be Ancient Egyptian, an antiquated form of writing such as shorthand, knowledge of building or repairing antique steam engines, programming COBOL, etc. PCs who graduated from this academy must be sure to have this skill in their repertoire.”
“ A certain tribe in a valley believes that the soul remains trapped in the body after death and is aware of it. So they treat their dead as if they are alive, talking to them and keeping them at home. They are used to the stink and for some reason are also immune to the diseases that this practise causes but outsiders are not so lucky.”