The Nightsisters of Dathomir

Fundamentally a splinter group of The Witches of Dathomir, the Nightsisters have had many incarnations over the millennia, forming when several Witches fall to the Dark Side, are exiled from their clans, and band together to form a new clan of their own. At times, they have even been numerous enough on Dathomir to form multiple clans. Initially, these rogue clans are typically small, and necessarily secretive, most often staking out territory far from the normal settled lands of their world, to avoid the notice of their former sisters. How they develop from there depends greatly on who leads them, what they learn of the Dark Side either on their own or by discovering hidden teachings of their forebears, and how long they can remain undetected by the clans that have rejected them.
The last century saw the rise and fall of two of the most powerful incarnations of the Nightsisters in Dathomir’s recorded history, in close succession. In the years leading up to the Clone Wars, an adept known as Mother Talzin came to power amongst her sisters and formed alliances with interests off-world by selling the services of her sisters as assassins and bounty hunters. Fragmentary reports from the war suggest that Count Dooku – leader of the Separatist Alliance – commanded a personal assassin who hailed from Dathomir for much of the duration of the conflict. Little beyond that can be reliably determined, due to the polluition of the historical record with propaganda and misinformation by the Empire in the war’s aftermath.
It is unclear precisely what changed on Dathomir during the Dark Times, or when, but Mother Talzin was apparently deposed, and replaced by another – Gethzerion, eldest daughter of the ancient Clanmother of the Singing Mountain Clan. Sometime after his seizure of power, Emperor Palpatine placed a blockade on the world of Dathomir, apparently to specifically contain Gethzerion and prevent her from challenging his power as Dark Lord of the Sith. This blockade persisted even after his death during the Battle of Endor, until it was broken by Jedi Knight Luke Skywalker and several of his companions, when they crash-landed on the world in 8 ABY. In the course of escaping Dathomir, Jedi Skywalker also precipitated the destruction of Gethzerion’s control of the Nightsisters, and Gethzerion herself.
The Nightsisters survived, in fragmented form, the death of their Clanmother, however, and continued under the leadership of lesser mothers for several more decades, even forming an alliance with the Shadow Academy until its destruction in 23 ABY. When Luke Skywalker, now Grand Master of a new Jedi Order, returned ahead of a new – or rather very old – Order of the Sith to the isolated world of Dathomir, the Nightsisters were destroyed. Many were killed by Skywalker and his allies, repelling their attack upon the unification ceremony that formed the Bright Sun Clan. When the Sith arrived, they discovered the power the Nightsisters wielded, and forcibly enlisted the survivors into the ranks of the Sith, spiriting them from their homeworld to the hidden stronghold the Sith had come from in secret. With their departure, it marked the first time in more than 200 years that there had been no Nightsisters operating on Dathomir. To date, there have been no confirmed reports of a new clan of them forming.