Faerzress

Faerzress is a special type of magical energy unique to the Underdark. Legends across the Material Plane claim that it originates back to the creation of every Underdark across every mortal world. Though its true origins have been lost to history, some scholars theorize that the magic disrupting effects of faerzress were put in place by Corellon Larethian and the other elven gods to keep the dark elves (who later became the drow) imprisoned after Lolth's banishment. In modern times, the intelligent denizens of the Underdark will often map areas for faerzress and build their settlements to use the faerzress-infused areas defensively against invaders.
Sections of the Underdark containing more faerzress than average contain several telltale signs of its presence. These areas can range anywhere from a few dozen feet across to miles long:

• Stone in areas suffused with faerzress always glows with dim light and give off comfortable amounts of heat.
• A creature in an area suffused with faerzress has advantage on saving throws against any divination spells. If a divination spell doesn't allow a saving throw, the caster must succeed on a DC 15 Constitution saving throw to cast the spell. Failing this save means the spell is wasted and has no effect.
• Any creature attempting to teleport into, within, or out of a faerzress-suffused area must succeed on a DC 15 Constitution saving throw. On a failed save, the creature takes 1d10 force damage and the teleportation attempt fails. Even if the save succeeds, the teleportation attempt can suffer a mishap as if the destination was known only by description, regardless of how familiar the destination actually is (see the teleport spell).
• When a spell is cast in a faerzress-suffused area, the caster rolls a d20. On a roll of 1, the spell has an additional effect, determined by rolling on the Wild Magic Surge table.

Dark Faerzress

While normal faerzress gives off a yellow glow, in recent decades a purple variety has been discovered in Nexus' Underdark. This faerzress seems to have the same magic disrupting effects as the conventional variety, though there appears to be more to it than that. Overexposure to it, either gradually over time or in a large concentrated burst, seems to cause madness in living creatures. The effects of this madness vary from creature to creature and are still largely undocumented, though the adventurers of the Thaig Expedition suspect the mad murderer Santaura has something to do with it due to her observed ability to manipulate faerzress.

Type

Ore/Mineral