Radiation

Nasty stuff. Either it turns you into a horrible apocalyptic zombie creature (e.g. Radiation Dogs), or enhances you with abilities far beyond those of mortal men. Often it does both (e.g. the pus-oozing plaguelord of Grambul).

Radiation is the by-product of a by-gone era of technology and is therefore found in regions that were the site of ancient wars, or abandoned cities that were powered by forgotten fuels (e.g. Extremewangokyo Ruins).