Deep beneath the earth, you find a vault of the Ancients from before the Silence. Inside, you find a sealed casket, deeply etched with dire warnings. Ignoring them, you break the seal. Inside, you find Armageddon's Blade.
The immunity to Armageddon provided by Armageddon's Blade is unaffected by the Orb of Vulnerability: the Orb of Vulnerability only affects enemy creatures in this case, while allied creatures retain their immunity.