“ 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.”
“ When was the last time a character caught a cold or flu? Real people get them every now and again even with solid heating and dry interiors. Your characters are out in the cold and wet, and even inside is not always dry and warm. Imagine having to stop your dungeon crawl, sitting in a tight defensive position, while you all are feverish.”
“ In a high canyon in the mountains, the players find a skeleton in a cage suspended from a pole. A few miles further, they find another, and a third contains a partially rotten corpse. The fourth contains a living man who looks as if he hasn't eaten in days. Turns out to be the local way of punishing criminals.”