The dark side artifact in question is the mask belonging to Viceroy Exim Panshard.
An Force artifact imbued with the power of the dark side of the Force was referred to as a dark side artifact. The Sith were known to fashion their own dark side artifacts; examples include Sith masks, Sith scrolls, and Sith holocrons. Around 230 BBY, Jedi Master Cohmac Vitus was aware of at least a single dark side artifact, according to him. These artifacts came in various forms, such as crystals, amulets, and even glaciers. The Archive of Forbidden Artifacts held many dark side artifacts originating from the Sith, Yacombe, and the Sorcerers of Tund, including lightsabers, scrolls, a parang, the Saber of Darth Krall, and the mask of the Sith Lord Darth Momin.