The Shadowdancers are a secret order formed after the Lightwar by Ameliorated Drow (Drow who's minds and souls were purged of corruption.) These Drow assist the Lightkeepers in maintaining the balance of light and darkness through the use of dark magi.
The Shadowdancers were formed in the years following the Lightwar by members of the Drow that had their minds and souls purged of corruption by Lightkeeper wizards in an attempt to revert them back to their Elvish selves. Most of these Ameliorated Drow decided to scatter about the continent, but some chose to remain and assist the Lightkeepers in their own way. Since they were still considered corrupted beings (as they were Drow) and could not join the Lightkeepers themselves, they formed their own organization called 'The Shadowdancers'.
The Shadowdancers already knew how to fight, most having fought in the Lightwar, and were already proficient in using dark magi. So why not use those abilities against those that would upset the balance of light and dark? Though their good use of dark magi would prove useful, it did not come without a cost.
Their minds and souls, though purged of the corruption they had suffered before, slowly but surely began to twist and change from the overuse of dark magi. Their fight to balance things would end up destroying them and turning them back into the regular, hostile Drow. Most of the Shadowdancers would suffer this fate, and would either be killed by their fellow Shadowdancers, their Lightkeeper comrades, or by suicide. Those that did not die would return to their Drow brethren in the Elven Realm.
Currently, there are few Shadowdancers left. But these remaining few still continue their fight to assist the Lightkeepers in maintaining the balance. Even at the cost of their own lives.