Laranna Fain while affected by the plague
The Dark Plague was a disease that was influenced by the Force and engineered by the Sith Lord known as Terrak Morrhage. To turn them against the Jedi Order, Morrhage employed the plague to corrupt the minds of Jedi Masters throughout the galaxy, manipulating them into fighting.
Although Morrhage was ultimately defeated, his spirit took control of the fallen Padawan named Parkanas Tark during the era of the Cold War, and he once more utilized the Dark Plague to corrupt the Jedi Order.
Parkanas Tark, who adopted the name Vivicar, had come to possess the knowledge of Morrhage's Force-based plague. This sinister technique instilled insanity into those whom Lord Vivicar had previously known, transforming them into puppets controlled by the Sith Lord, including Laranna, the daughter of Duras Fain. The symptoms involved a strong belief that "The darkness [was] coming", along with the conviction that actions that would normally be unthinkable for the affected Jedi were necessary to prevent it. As his influence expanded among the members of his former team, a young Jedi Consular stepped forward to confront Lord Vivicar. This young Consular, a Padawan of Yuon Par, discovered an ancient shielding-technique capable of freeing individuals from Lord Vivicar's control. This technique was subsequently used to liberate the Jedi Masters from Lord Vivicar's domination, and it also rendered the Consular immune to the plague.