Chance on hit: Blasts up to 3 targets for 150 to 250 Nature damage. Each target after the first takes less damage. Use: Transforms Thunderstrike into Shadowstrike. (1 Min Cooldown)
Sell Price: 8 73 72
Source
Thunderstrike is the transformed version of Shadowstrike.
Patch changes
Patch 1.8.0 (10-Oct-2005): Shadowstrike and Thunderstrike will now remember the enchantments and durability data they possessed when they transform.