Star Wars' Jedi Master Oppo Rancisis, devout member of the Jedi High Council, was a master strategist during the Republic era and the Clone Wars. He spent much of the Clone Wars on Coruscant, where he coordinated Republic forces through the galaxy during major events such as the Defense of Kamino and the Battle of Zaadja. Rancisis was also a highly respected figure in the Republic, regularly conferring with Supreme Chancellor Palpatine and serving on the Council of Reconciliation. But while Rancisis' history is notable, he mastered a Force power even more impressive than these accomplishments.
This Force power was known as Malacia. It originated from Star Wars Legends and isn't currently canon; however, it's frightening. Malacia can literally make one's stomach churn, as it induces strong dizziness and nausea in enemies by turning their equilibrium against them, completely incapacitating the target temporarily.
Rancisis was also a strong proponent of Malacia, despite its status as a unorthodox power. Despite causing no physical harm, some of its effects were so strong that it caused targets to vomit. While Malacia completely debilitated an enemy, it was not considered a Dark Side power because it did not damage the body and it transformed a target's energy rather than using the energy of the wielder.
In Ryder Windham's Jedi vs. Sith: The Essential Guide to the Force, Rancisis cleverly explained that the technique simply interrupts the regular biological processes by manipulating the blood flow of a target. According to the Jedi Master, an organism's natural movements are already enough to cause nausea, but this is prevented by the body's well-coordinated systems. An interruption in this flow affects the body and mind at once, taking out its target without causing permanent harm like aggressive Dark Side Force powers.
"Imagine a sentry guarding a post that you must bypass," Rancisis elaborated. "The sentry may be standing still, but his mind is alert and his systems are functioning. Everything is in motion. Blood flows, muscles tense, food is digested, and atmospheric gases are inhaled and exhaled. All that motion is enough to make him dizzy and queasy, and by focusing on that flow of blood, you can make that happen. The sentry will be so overwhelmed that he will be disabled, yet will suffer no permanent side effects."
While Malacia had support from Rancisis, the power was widely controversial among the Jedi Council, with some perceiving it as violent. Others disliked the fact that it only affected organic beings and preferred the use of Force Push or affect mind to achieve Malacia's results. The only other Jedi Master known to have used to the technique during Rancisis' era was Plo Koon, although he never mastered Malacia as well as Rancisis. Use of the power was rare in the Old Republic as well; however, Jedi Master Asli Krimsan recorded Malacia in her holocron.
Despite its divisive nature, Rancisis taught the practice for many decades and even recorded the practice in the Great Holocron in Legends. Virtually none of his pupils were capable of mastering the technique, but Rancisis' teachings would eventually end up in the hands of The New Jedi Order. Jedi Masters such as Tionne Solusar thoroughly documented Rancisis, which prevented Malacia from falling into further obscurity. While Rancisis' efforts during the Clone Wars were ultimately futile, his teachings on Malacia helped keep his legacy alive.