During the Clone Wars, Jedi Master Yoda encountered the Force Priestesses on a planet in the heart of the galaxy, where they put him through a series of trials. The Priestesses represented Serenity, Joy, Anger, Confusion, and Sadness, respectively, and nothing was found behind their white masks.
The Priestesses existed in a state between the living Force and the cosmic Force, and they could manifest themselves before the living at will.
The trials they put Yoda through forced him to face the personification of his hubris, resist great temptation, and finally, travel to Korriban, the homeworld of the Sith, to pass the ultimate test, which was beyond the Priestesses' control.
When Yoda's trials were complete, the Priestesses deemed the Jedi Master able to retain his identity after death.
- Star Wars: The Clone Wars – "Destiny" (First appearance)
- Star Wars: The Clone Wars – "Sacrifice"