Shadowguard

The Shadowguard are ethereals who have heeded the call of the Void and become Void ethereals. They seem to be related to the Ethereum. They were drawn to Mac'Aree on Argus by the Void energies of the naaru L'ura. They stormed the Seat of the Triumvirate and established a base named Shadowguard Incursion. There, they used Void harvesters to call the Void to Mac'Aree, but they were stopped before they could plunge the entire city into shadow and cause all of Argus to fall to darkness. The darkness they cultivated manifested into crystals of pure void, a resource the Shadowguard coveted. The Shadowguard also succeeded at creating Void-infused Broken whose mind did not fall into madness. Shadowguard Abyss Callers attempted to summon another void lord through the Umbral Locus, but their ritual was interrupted.

Another Void ethereal named Locus-Walker stood in opposition to them. He had hoped to find more ethereals among the Shadowguard who possessed the necessary strength of mind to resist the Void and was disappointed to find such an utter lack of resistance.

Unnamed

 * Presumed members
 * Grand Shadow-Weaver
 * Umbral War-Adept

Notes and trivia

 * Some Shadowguard NPCs have female voices, though without a female model to match.
 * In early 7.3 PTR, Void-Blade Zedaat was a world boss and not a rare mob. His dungeon journal entry read "Viceroy Nezhar's most trusted lieutenant, Void-Blade Zedaat has been charged with keeping the Legion and all others away from the Seat of the Triumvirate until his work can be completed".
 * Adjectives used to describe the Shadowguard's various Void creatures include "bound" and "enthralled".

Speculation
Since Nezhar's title is "viceroy", this means that he is ruling in the name of another. The true leader of the Shadowguard is unknown, or it might've been Saprish since he is called the "Ethereum-Lord of the Shadowguard".