Pictured is an Umbaran Shadow Assassin during the Crisis on Umbara.
Concerning Umbaran Shadow Assassins: These Umbaran warriors existed from at least the time of the rebellion against the Eternal Empire, participating in certain events across the galaxy. During the New Sith Wars, they functioned as Sith spies serving the Brotherhood of Darkness. The Umbaran Sith Academy served as their training ground. They typically wielded the Force pike as their weapon of choice.
These Shadow Assassins possessed the capability to conceal their presence, not only in the Force but also from physical detection through senses like sight and hearing. It was implied that they could also use the dark side to kill with relative ease. However, their combat effectiveness diminished significantly if their core strengths of surprise and stealth were negated.
A minimum of eight Umbaran Shadow Assassins lived through the Thought bomb event, which resulted in the near-total annihilation of the Sith at the Seventh Battle of Ruusan. These survivors were enlisted by Hetton, a Force-sensitive individual and Sith follower, for his personal agenda. Nevertheless, the Sith Lord Darth Bane eliminated them all when Hetton attacked him, in an attempt to secure his position as an apprentice to Bane's apprentice, Darth Zannah.