Night Reaver

Night Reaver is a two-handed axe. Double-edged and weighted for extra damage, this axe is also afflicted with a shadow curse that may cause extra damage. It's high-end damage and proc make an excellent axe for any low level warrior.

Source
Night Reaver is dropped only in Shadowfang Keep. It isn't dropped by any particular mob, defined as a world drop, but rather is found throughout the keep, albeit at a very low drop rate.