• Reinforced Shadowstrike
• Item Level 245Disenchants into:
  [Abyss Crystal]: 1-2
• Binds when picked up
  
• Polearm
• Two-Hand
  
• Speed 3.10
• 634 - 951 Damage
• (255.6 damage per second)
• +120 Agility
  +126 Stamina
• Durability 120 / 120
• Requires Level 80
• Equip: Improves critical strike rating by 73.
  Equip: Increases attack power by 157.
  Equip: Increases your armor penetration rating by 89.
  Chance on hit: Steals 100 to 180 life from target enemy.
  Use: Summons a new Reinforced Thunderstrike.
• 
• Sell Price: 29 87 2

Can be used to summon a  [Reinforced Thunderstrike].

Source

This item drops from Onyxia in the 25-man version of Onyxia's Lair.

Patch changes

• Patch 3.3.0 (08-Dec-2009): No longer has a cooldown to create Reinforced Thunderstrike. 
  
• Patch 3.2.2 (2009-09-22): Added. 
  

External links

• Battle.net (EU)
• Wowhead
• Thottbot
• WoWDB