Umbaran Shadow Assassins were Sith spies employed by the Brotherhood of Darkness during the New Sith Wars. They trained in the Umbaran Sith Academy. Their preferred weapon of choice was the force pike.
Shadow Assassins were able to mask their presence, not just in the Force but also from physical senses such as sight and sound. It was also hinted that they had the ability to kill using the dark side with minimal effort. They were not as skilled at combat if their primary advantages, surprise and secrecy, were neutralized.
At least eight Umbaran Shadow Assassins survived the Thought bomb that killed virtually all the Sith at the Seventh Battle of Ruusan. They were recruited by a Sith-following Force-sensitive known as Hetton for his own personal use. However, they were all killed by the Sith Lord Darth Bane when Hetton attacked him, hoping to secure his apprenticeship to Bane's own apprentice, Darth Zannah.