If you picture the Koxiux the Imperceptible camp as one end of a horseshoe, Xiox is on the other end of the horseshoe. Download the in game map from map fiend and you'll understand what I'm talking about. It has Koxiux's camp listed on it, and the horseshoe will be obvious.
Downed him in maybe a minute as a 70 necro with lifetaps and the 67 pet with 2 Swarm of Decay archers and lifetaps. As easy as Koxiux. Pet pull with the 44 pet and Calliav to absorb the blows and /pet hold AA to bring back the surrounding mobs one at a time. Then finish him and one add off. Dropped the Faceguard. However you can buy better than the mask and weapon in the bazaar these days. Not worth the wait imo. But the Wand of Imperceptibility off Koxius is.