The Dark Orb, so named due to its shaded color, was a singular piece of magic, either Ayleid or Daedric, that was used by Umaril the Unfeathered and the Aurorans during the Auroran Crisis. Completely round and pulsing with dark energy, the Orb was a powerful tool in sustaining Umaril's army within his fortress of Garlas Malatar. Contained on the Ceysel level of that place, the Orb somehow allowed the Aurorans under Umaril's command to return to life immediately after being killed, whereas their spirits would normally have to be revived within the Realm of their Daedric Prince, Meridia. Due to this distinction, it is highly plausible that the Orb was Daedric in nature, perhaps a gift from Meridia herself to Umaril.
The overall purpose of the Orb is unknown, but it did prove its worth during the Battle of Garlas Malatar, where the Knights of the Nine, under the command of the Hero of Kvatch, attacked Umaril's stronghold in an effort to stop the Crisis. When battling Aurorans on the Ceysel level, the Knights experienced the power of the Orb as every Auroran they cut down rose seconds later to fight on. Finding the source of the Aurorans' power, the Hero ascended to the Orb's resting place, where he fought and killed the Orb Guardian. The Hero then destroyed the Dark Orb, shattering it and releasing its power. When the Orb was broken, time stopped in Ceysel, and both the Aurorans and Knights vanished. The broken pieces of the Orb hung suspended in the air, leaving the Hero alone to continue on to Umaril's throne room. While these were the immediate effects of the Orb, it is unknown what exactly it was, or what its purpose truly was.