Dvergar lived in the Underworld long before the dokkalfar appeared, long before the elven children turned into what we know as 'drow' - creatures of the Underworld. So-called 'elementals', the dvergar do not have the ability to bend mana to their will, nor to produce mana, but they are still affected by their environment just like the fae, their appearances different from one area of the Underworld to the next. (We do not currently know anything more about what 'elementals' are, so for the purposes of the DT rpg, the only effect until notified otherwise is on their appearance as described in this post.)
The typical dvergar is short, around 4-5 feet tall, stocky and has skin the color of raw rock. Their skin color varies with the rock types found in the area where they were born, thus giving Chelian-born dvergar a rather uniform skin color while wildborn dvergar can have highly varied skin colors. A dvergar is typically balding, with body hair resembling organic roots. A dvergar born in an area with a lot of light will have large eyes, whereas a true dvergar from the darkest depths will have tiny, beady black eyes. Some will ocasionally call the larger-eyed dvergar 'gnomes', a derogatory term derived from one of the words the elves used about the Underworld's original inhabitants.
Dvergar are known to be excellent crafters. They have a higher percentage of specialists than elves, for example, when it comes to metal and rock working. Unless the elves augment their work with earth or metal sorcery, the dvergar are both better miners and better smiths.
The dvergar are the only race with knowledge of explosive powder and how to make it. It is a well-kept secret which they have shared with no other race, and they guard the knowledge jealously. While it is fairly common for a dwarf to have explosive powder (provided he has a job in which he needs it, be it miner or warrior), the knowledge of how to make it is not held by many.
The dvergar do not have handguns or muskets. They do, however, have small cannons which can launch deadly cannon balls. They will break through a single mana shield and even the best made armor, but mana specialists working together can deflect them with some effort. They also have bombs of varying efficiency, most notably small pouches containing irritants which make the air difficult for non-dvergar to breathe. Gas masks and filters exist which can prevent this from being a problem. Generally, dvergar wear light, worked chitin armor, or kiri'su leathers. They prefer to carry ranged weapons as well as melee weapons whenever possible, short range blades being a disadvantage when fighting drow.
Dvergar society is diverse, with many different factions. While most still hold a grudge against the surfacers who invaded the Underworld, the dvergar are not united in their hatred of drow. Some dvergar are part of active resistance, most either keep away from drow or do the exact opposite, making a profit where once only hostilities existed. The Chelian Dvergar Association is an example of the latter; Acting as dvergar liaison for Chel'el'Sussoloth the association offers mining expertise, guides and run a dvergar mail service allowing Chelian dvergar to keep in touch with their cousins elsewhere. They also provide counseling in cases where drow have begun mining in dvergar territory, or where dvergar have come to reclaim their old land.
The maximum age of a xuile'solen is less than 200 years out in the wild, or in their own society. A captive xuile'solen can live nearly as long as a drowolath commoner, as civilization offers a less risky environment, more food, and a pool of mana. Even given the best of conditions, due to their stunted aura a xuile'solen can never live as long as a 'lath given the same conditions.
There is one official settlement of xuile'solen around Char, otherwise they are usually found across the underworld, in the suburbs of big settlements.
The xuile'solen are very rare, both as slaves and especially as free citizens. They are generally the same height as 'lath but thinner, weighing less.
Being eyeless, xuile'solen possess a superior sense of smell and taste, and also have better hearing than drow. They do not have the ability to sense or 'see' auras.
Xuile'solen have a superior resistance to pure mana only. They are incapable of using mana arts.
==Kotorcs and Noz
A small tidbit of information can be found here: http://www.drowtales.com/wordpress/?p=2824
Kotorcs are featured in MA when Ariel and the Sarghress take over the Black Dragon Tavern, and in a few other scenes, so look through the newer comic chapters for them. Noz have only been featured once so far I believe, in the page that this news article refers to.
==Ne'kalsaider and driders in general
Ne'kalsaider are natural born driders, and they suffer no mental illnesses from their state as it is the only one they know. They are as strong or in some cases even stronger than drow, and they can work mana arts, but they rarely receive any schooling except what their parent(s) give them. It is rare for a Ne'kalsaider to be raised by their actual egg-mother, as there have traditionally been very few fertile Ne'kalsaider.
The Ne'kalsaider owe their existence to the drider guardians of old, but the art of creating drider guardians has long since died out, and the guardians who survived were never meant to be able to breed. Somehow, this happened anyway, and the Kyorl'solenurn see their very existance as an abomination.
For the purposes of the DT rpg, half-Ne'kalsaider of any type do not exist.
As for other driders:
It used to be that we heard about waeliniders (the 'created') and streekaider (the mad). But these do not really exist anymore.
The drider guardians were popular once, and many brave warriors were transformed by skilled practicioners at death's edge, to save them and make them able to fight once more. But the drider guardians became unpopular, and the art of creating them died out completely. No one alive today knows how to create one.
The Ne'kalsaider are the offspring of those few guardians who were able to breed, and who hid their very existence from the mighty powers of Chel'el'Sussoloth for centuries.
Somewhere along the line someone (probably a Jaal) invented a new way to fuse spiders with drow, but this new method created mindless guardians of the same nature as the Vloz'ress fake nagas. They are basically the streekaider of old, but controlled by whoever owns them, rather than wild and mad.
The Beldrobbaen view these new mindless driders as vile, and would never submit one of their males to this process. Thus it is probably fair to assume that the old tradition of turning the male into a drider guardian once he'd fathered a daughter has been lost for some time, along with the loss of the knowledge of this transformation in the first place.