- "A skilled shadow killer can vanish from sight."
Shadow killer was a Nightsisters rank and specialization. It was one of three categories of mercenary skill offered to offworld clients by the Nightsister clan, the other two being those of hunter and warrior. All Dathomiri mercenaries, which included those from the ranks of both the Nightsisters and the Nightbrothers, were chosen from the successful endurance of the trials of Selection.
A shadow killer was an assassin from Dathomir. They carried weapons that were silent and easy to conceal, such as daggers and darts dipped in poison. They also wore black wraps to help them blend in with the dark. Shamans of the Nightsisters such as Talzin could summon a mist (a cloak of spirit ichor) that allowed these killers to walk midway between the physical realm and the spirit realm.
In 21 BBY, Clan Mother Talzin allowed Asajj Ventress to use the Shadow Killers' mist (ichor cloak) to avenge herself of her former master, Count Dooku, with the aid of two of the coven's finest warriors, Karis and Naa'leth. Talzin also provided Ventress with the poisoned dart of the assassins.
According to Galactic Emperor Palpatine, the stealth skills of the shadow killers could easily rival those of the Defels agents. This is why the Emperor ordered the Imperial Security Bureau to conscript from the Nightsister assassins some time after 19 BBY.