Elephants crossing the seas!
It is not an infectious disease, but it is a plague upon the world.
For it spawns villains. And not your garden variety villains, but epic villains, master villains of the most dangerous kind Evil Geniuses.
Pnathic sorcery has existed for ages, crudely used by magi who no idea the true forces they were fumbling with.
An article concerning the nature and role of druids in an RPG enviroment.
Of creatures great and small
The Omen Plague has other names. It is known as The Star Plague and even The Mundane Plague. It is still with us today, now known by the common name of the Shaking Death. To set the stage, the stars were aligned in all the wrong signs. Everyone new something bad was going to happen. When winter set in hard and early, they thought that was it. They were wrong.
Plagues and other great diseases are important parts of history and some settings. They defy man and may even defy God in their swift and terrible punishment upon the body of society.
A race of beings actually IS invunerable while in adolecence. They age, but cannot be killed. A miniority of the race (1 in 20) does not become invunerable, but rather becomes immortal at some point in thier adolecence, and ceases aging while being vunerable to death in all the normal ways. Another minority (also 1 in 20) Permanatly becomes invunerable after adolecence, but ages twice as fast as the race normally does. There is no known way to test for which of the three traits an individual manifests and the three traits cannot mix, as they are tied to the same gene, as it were.