Illusion (Sith Magic)

Illusions, or mindforms were dark side Force manifestations, that when conjured through Sith Magic, created visible, lifelike astral projections of whatever the conjurer desired. The illusions touched all of an individual's sensory perceptions, and only through concentration on the Force was an individual able to perceive them as being false. By simply gesturing with one's hands, a magician could create whatever manifestations she desired. As an application of the dark side, sorcerers tended to create hideous forms of serpents and other creatures to torment victims. Playing on all the victim's senses, the illusion could seemingly attack individuals, should they actually believe the apparition to be real. However, the illusion could be undone should the victim cease to belive it exists. The illusions could also be undone if the conjuring sorcerer is interrupted by a powerful light side attack.

This technique was believed to be lost until it was rediscovered by Darth Sirena.

Information courtesy of Wookiepedia