Tenebrae's curse, a terrible affliction, was unleashed at the same time as the Battle of Zakuul took place. The Commander of the Eternal Alliance expunged the spirit of the Immortal Emperor Valkorion from their consciousness, which led to the Emperor's Wrath Scourge and the Jedi Knight Kira Carsen discovering and destroying his original Sith body. This action set off a trap that Tenebrae had prepared: the destruction of his physical form was connected to a Sith ritual etched onto his body centuries before, causing the release of the plague into the atmosphere. Because Scourge and Carsen had previously experienced similar effects from the emperor, they were immune to the infection, but they were rendered comatose for over a year.
Around 3628 BBY, Jedi Master Satele Shan spearheaded an operation to rescue Scourge and Carsen. However, the plague remained active, and Shan and her followers unknowingly became infected. Within a matter of days, they were plunged into a nightmarish sleep, gradually merging into a collective hive mind. After being successfully rescued by the Jedi, Scourge and Carsen apprehended them and placed them in quarantine aboard a transport vessel that was traveling on an unknown course through uncharted sectors of the Outer Rim Territories.
Kira later came to the realization that the ritual inscribed on Tenebrae's original body was not a plague, but rather an imprint, an echo of his original self designed to manifest upon the destruction of both his body and spirit. Even though the imprinted spirit did not retain the memories of the original, it still possessed the same abilities.
The symptoms of the plague appeared to be exclusively psychological in nature, with no physical alterations reported. These symptoms included coma, nightmares, and delusion (the afflicted becoming lost in a dark side hive mind). Even individuals with great strength in the Force were easily overwhelmed by the plague. Individuals who had previously been affected by Tenebrae in similar ways, such as the Children of the Emperor or members of his power base, were resistant to the disease, only experiencing a comatose state upon exposure.
The truth was revealed that the ritual was not a plague, but instead an imprinted spirit of Tenebrae. This spirit manifested and sustained itself on the memories and impressions of Satele and her students, enabling the Emperor to be reborn once more, but without the memories of his original self. However, by analyzing the memories of people near him, this clone of Tenebrae began to learn of the real Tenebrae's various exploits during his lifetime. However, this knowledge did not change his personality. Instead, the clone condemned the original Tenebrae for having become "complacent" and "distracted by mortal concerns; Empires, wars. Even a family." He stated that he had seen how that path led to the original Tenebrae's destruction. The imprint then declared that he would conquer the Galaxy for himself.