Duergar should be treated as Fighters for determining their BAB. They are able to attack twice per round by dual-wielding axes. The second attack is at a -2 to-hit penalty — but if the first attack hits, the penalty for the second drops to -1.
Anytime five or more duergar are found together, one of them will be a leader with 5-7 HD (35-40 HP, and a 70% chance of having arcane or clerical spells. A defeated leader is worth 800 xp.
Millenia ago, the duergar were a clan of shield dwarves in the dwarven kingdom of Barakuir, located within the ancient realm of Shanatar. Clan Duergar, which venerated Laduguer as their patron, was an ambitious and powerful clan, believing that they should lead the kingdoms of Shanatar themselves.
When they were denied following the Second Spider War, Clan Duergar turned away from the other dwarven clans, paying only lip service to Shanatar's rulers. This proved a mistake when the mind flayers of Oryndoll, seeing the isolation of Barakuir, attacked the realm in about 8100 DR, enslaving or killing most of the population.
Most duergar worship Laduguer.
During their captivity, which lasted for generations, the mind flayers performed many cruel and unusual experiments on the dwarves.[10] It was during this harsh period of their history that the duergar emerged as a distinct subrace.[15] Eventually, they rose up against their captors and gained their freedom from the mind flayers.[10]
Now free, the duergar carved out a new home for themselves beneath the Great Glacier, founding the city of Gracklstugh. The Deepkingdom spread rapidly through the northern reaches of the Underdark, reaching its peak before a war with the quaggoths of Ursandunthar caused it to enter a gradual decline, battling the remnants of the nation and urged on by drow for centuries thereafter. Since their taking of Gundgathol, their numbers are again waxing.