Duergar, also known as gray dwarves, are a subterranean race. They are close kin to dwarves, but with adiabolic taint to their blood. They now carve out their existence in the Underdark, often near volcanoes. Their kinship to surface dwarves can be compared to that of the drow to surface elves.More information can be found here and here .
Duergar recieve ELC +1 (or none?).
Constitution +2, Charisma -4.
Immunity to paralysis, phantasms, and poisons.
Skill affinity: +4 Move Silently, +1 Listen/Spot.
Invisibility once/day, Light Sensitivity.
Favored Class: Fighter