Part of the Bonescythe Armor set:

The set gives these bonuses as more pieces are worn: 2: Your normal melee swings have a chance to Invigorate you, healing you for 90 to 110. 4: Your Backstab, Sinister Strike, and Hemorrhage critical hits cause you to regain 5 energy. 6: Reduces the threat from your Backstab, Sinister Strike, Hemorrhage, and Eviscerate abilities. 8: Your Eviscerate has a chance per combo point to reveal a flaw in your opponent's armor, granting a 100% critical hit chance for your next Backstab, Sinister Strike, or Hemorrhage. Set Details | All Sets

Quest Reward from:

Level	Name	Start	Rewards
60	Bonescythe Pauldrons  (Raid) Horde and Alliance Naxxramas	Rohan the Assassin <The Scarlet Crusade> Eastern Plaguelands

Disenchants into

Name	Value	Drop%
Nexus Crystal	1 Copper	100.0%