Faerzress

Mild radiation found in the Underdark, faerzress is a remnant of primordial magic that helped shape the Underdark itself. It may interfere with the casting of teleportation and divination spells. This radiation gives some races innate abilities. For instance, the ability of drow to levitate and invoke magical darkness, as well as faerie fire.

Drow seek out areas with strong faerzress to build their cities and outposts, in order to keep others from scrying on their activities or teleporting inside their cities. Drow also use faerzress to create magical items and artifacts.

Areas of high faerzress concentration sometimes manifest physical signals, ranging from subtle shifts in temperature to visibly glowing rock formations. Drow-made magical items fashioned in the Underdark gradually use their enchantment within a few days of being removed from the Underdark.