“ The PCs see a large oak tree, a curious species of yellow and black butterflies swarm around it. Upon further inspection they find that the tree is hollow and that there is an underground cave in it from which the butterflies appear. Will they inspect this strange cave?”
“ What if some crazy wizard created an artifact that empowered rodents that touched it with one random supernatural power? Preferly right out of the pages of your favorite four-color. (But only one power!) This item does not convey any sort of intelligence boost.”
“ 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.”