Star Wars: Sith Holocron Files: Darth Sidious' Teachings
agentbsmit for Sith Warrior (Ghost) #2
A Sith warrior was a type of Sith active before the Rule of Two.
During a voyage to the Sith homeworld of Moraband, Jedi Master Yoda encountered undead specters of these warriors.
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.
*Note* The ideal voice to go for is something raspy like a whithered ancient spirit speaking from beyond the physical plane. See the Sith Ghosts from Star Wars: The Clone Wars for reference: https://youtu.be/TjQH8a5jdMY?t=1m57s
"He has the hunger."
"Darth Vader! He carries the blood of Darth Vader within his veins."
"He must be destroyed."