Mortanius's Death Orb, or the Orb of Mortanius, was a Pillar token gifted to the Death Guardian, Mortanius the Necromancer, by the Pillar of Death. Following Mortanius's demise, Kain recovered the token, and used it to momentarily restore the corrupt Death Pillar. The Orb appeared only in Blood Omen: Legacy of Kain.
Possessed by the Dark Entity, Mortanius met with Anarcrothe and Kain at the Pillars near the conclusion of the events of Blood Omen. Mortanius killed Anacrothe, and battled Kain. After a brief skirmish, his body was fully taken over by the Entity, and ultimately destroyed by Kain.[1][Blood Omen/11][2] Kain claimed the Orb as Mortanius's token of power, noting its unusual abilities before placing it at the base of the corrupted Pillar of Death. The Pillar accepted its offering, and, for a brief moment, was restored.[Blood Omen/11][Blood Omen/Miscellaneous] Soon after, when Kain refused the sacrifice, it collapsed.[3][Blood Omen/12]
"Before the Pillar of Death, I laid the Orb of Mortanius."
Kain notes that the Death Orb assuaged not only his lust to feed, but also his "rage" – and Kain's madness stemmed from Nupraptor's corruption of the Pillars.[Blood Omen/Miscellaneous][Blood Omen/12][Soul Reaver 2/2] The Orb may have thus counterbalanced the corruption's effects for Mortanius, too, and might have contributed to his lucid nature even following Ariel's death – whereas his fellow Circle of Nine succumbed to insanity and wreaked havoc in Nosgoth.[1]
Mortanius's Death Orb and Anacrothe's Scales are, technically, optional items. Since they can only be collected in the fight with the Dark Entity – and since that fight ends once the Entity is defeated, irrespective of whether the tokens are obtained – it is possible to conclude the game without them ever entering Kain's inventory. Storywise, though, Kain does definitively use them both to restore their respective Pillars, before refusing the sacrifice.[Blood Omen][3]
The Death Orb, much like Moebius's Hourglass, has no presence in the Legacy of Kain series beyond its debut in Blood Omen: Legacy of Kain, despite the reappearance of its owner – Mortanius – in Legacy of Kain: Defiance. Mortanius is not depicted with it in the latter game.[Blood Omen][Defiance]