The Night Blade is an epic dagger with an armor reduction proc.
Duel wielding The Night Blade can result in accumulation of up to 6 charges of the armor debuff.
Patch 2.1 Edit
As of Patch 2.1, the Night Blade has received a nerf and a buff. The DPS (damage per second) has increased to 94.2, but its proc has been changed to 62 critical strike, making it still a balanced weapon.