Undead Artix is the Mirror Realm counterpart to the main universe's heroic Artix von Krieger. In the Mirror Realm, unlike the friendly, undead battling-loving Artix in the main world, Undead Artix is an evil DoomPaladin who is the greatest undead and is the greatest champion of the evil King Alteon the Imbalanced, whose undead army he leads. He holds the most evil weapon ever, the ShadowReaper of Doom. Undead Artix lives in Skullcrusher Mountain with Alteon the Imbalanced and his undead armies, along with one of his lieutenants, Scarface.
Undead Artix was ordered by King Alteon the Imbalanced to guard the cage where he kept Mirror Drakath's friends, the Lords of Order, imprisoned. According to Paul and Storm, the ShadowReaper of Doom wielded by him was the last of the three reagents needed to destroy the cage empowered by Alteon's shadow magic. With the help of Jonathan Coulton, the AQWorlds heroes managed to defeat him, knock his helmet off, and claim his ShadowReaper of Doom. Drakath and the players then used it, along with the other two reagents, the Crown of Blood and the Platinum Feather, to destroy the cage and free the Lords of Order. When the heroes got back to their universe later afterwards, Artix became jealous of them upon finding out that they fought Undead Artix and didn't even take him to fight him, wanting to fight Undead Artix despite not knowing that he wouldn't be able to do so because by going to the Mirror Realm, he would have to switch places with him instead.
Later, when the heroes were fighting alongside Dage the Good against Alteon's undead army in the Overworld, it was revealed that Alteon the Imbalanced revived Undead Artix by recovering his parts and had made some improvements to him ever since the last time his plans were foiled by them. He commanded him to kill the heroes, but even with his improvements, Undead Artix was defeated and beheaded by the heroes once more. They vowed that they would give his parts to Dage the Good so that he could free Artix's soul once and for all.
- Undead Artix is the only villain in AdventureQuest Worlds whose defeat involved him being beheaded.
- He has a more difficult version of himself known as Super Undead Artix, which drops two extra items in addition to the ones already dropped by his standard version; the ShadowReaper of Doom and Mirror Drakath's armor.