Mission to Serenno (Nightsisters)
A mission unfolded on Serenno in 20 BBY after Darth Sidious commanded his apprentice, Count Dooku, to eliminate Asajj Ventress. Following Ventress's survival of Dooku's assassination attempt, she sought vengeance by enlisting the support of her fellow Nightsisters. Ventress journeyed to Serenno with Karis and Naa'leth, where she attempted to assassinate Dooku. However, the Sith Lord successfully defended himself, overpowering his attackers.
The mission
Utilizing invisibility, Asajj Ventress, accompanied by two Nightsisters, infiltrated Tyranus's palace. Ventress employed a poison dart, striking Dooku's neck and causing blindness. Despite this, he maintained awareness of their presence through the Force, initially mistaking them for Jedi. The Count declared that his senses extended beyond mere eyesight. Subsequently, Dooku launched a swift attack on Ventress, initiating a lightsaber duel within the Count's bedroom. The other Nightsisters joined the fray when opportunities arose, yet the Count's skillful and adaptable swordsmanship kept them at bay. Ventress and one other aggressor pressed the attack, while Dooku maintained a strong defense, maneuvering through the corridor until they reached his office. Cornered in his office, Dooku faced the combined assault of the three adversaries. Despite his best efforts, his stamina rapidly depleted against the multiple opponents. Ventress, maintaining her concealed presence throughout the confrontation, successfully disarmed the Sith Lord by using the Force to push him into his desk. As she prepared to deliver the final blow, Dooku, simulating exhaustion and vulnerability, retaliated by unleashing Force lightning upon Ventress and her companions, propelling them out of the window and over a cliff, thus ending the assault. Nevertheless, the three Nightsisters survived and returned to Dathomir.
Aftermath
Tyranus, misled by the attackers' use of Jedi lightsabers, mistakenly concluded that the Jedi had attempted to assassinate him. Seeking self-preservation, he sought a new apprentice to replace Ventress (whom he wrongly believed to be dead).
Following the failure of their direct attempt to eliminate Tyranus, the Nightsisters devised a new strategy involving a double agent. To execute this plan, Mother Talzin contacted Tyranus, offering a Nightbrothers warrior to serve as his new assassin. Tyranus, perceiving this as a chance to acquire the apprentice he desired, accepted the offer. After selecting Savage Opress as their pawn, Talzin presented the imposing Zabrak to Tyranus, who was pleased with his new warrior, remaining unaware of his true allegiances.