"…each successive Sith Lord improved on it, Tenebrous and his Master most of all, though they wasted years attempting to create a targeted virus that could be deployed against the Jedi, separating them from the Force."
―Darth Plagueis discusses the Sith Master's and Tenebrous's role in advancing the Grand Plan[src]
Darth Tenebrous's Sith Master burdened the Bith with studying the Force, which Tenebrous viewed as simple. The Bith eventually came to believe that the Force was an energy source that he could manipulate in order to achieve his goals. After reading the prophecies in the Journal of the Whills regarding the Chosen One who would bring balance to the Force, Tenebrous was determined to use a variation of the essence transfer—a Force technique that enabled its user to transfer his or her consciousness into another body—at the moment of the individual'sbirth, thus making himself the Chosen One.[3] Around 167 BBY,[1] when Tenebrous's calculations for his scheme were complete, the Twi'lek was slain by his apprentice, who went on to take the MuunHego Damask as his apprentice, naming him Darth Plagueis.[3]
Plagueis, the Sith Master's eventual successor, acknowledged the Twi'lek's role in advancing the Grand Plan to topple the Jedi and the Republic and opening a rift in the Force. The Muun Sith Lord recounted the Master's and Tenebrous's achievements to his apprentice, Darth Sidious.[2]
The Twi'lek Sith Master was dedicated to the Sith initiative to topple the Jedi and the Republic. Despite the Master's and Tenebrous's attempts to create a virus that would separate the Jedi from the Force, they ultimately abandoned their efforts.[2] Tenebrous viewed his Master as simplistic and tottering.[3]
Tenebrous's Master was capable enough to cause a rift in the Force that enabled the Jedi Order to feel the dark side's presence for the first time since the New Sith War's final battle.[3] However, the Twi'lek was not able to withstand Tenebrous, who slew his Master.[3]