The Sith warrior wore an outfit that obscured all features, including a mask with a vertical slit in the middle. The warrior also wore a hood that stretched far above its head. The gloves worn by the warrior were elongated with claw-like digits.
Although the specter of these undead warriors were illusions, they were described as "evil" and were made from the Dark Side of the Force. They emanated black smoke, similar to that seen in the Valley of Extinction on the Force Planet and in the Cave of Evil on Dagobah, both locations strong with the Dark Side.
These Sith warriors were part of the Sith Order active during the time of the Old Republic. They existed at some point before Darth Bane enacted his Rule of Two, mandating only a Sith Master and an Apprentice at any one time.
During a spiritual quest in the middle of the Clone Wars, Jedi Master Yoda traveled to Moraband, then a dead and long-abandoned world. On his way to the greatest Sith temple in the Valley of the Dark Lords, Yoda was surrounded by 17 specters of these Sith warriors. These were conjured by the Force Priestesses as part of his test to find a way to exist beyond death. The specters mocked his quest and warned that there was only nothingness after death. They then threatened to reveal Yoda's location to the living Sith and slammed into him, leaving repercussions in the Force. Their act led to Darth Sidious and Darth Tyranus sensing Yoda's presence on the Sith world.