Scourgebane Draught

Scourgebane Draught is a one-use potion that gives you a temporary buff to your attack power against undead. As a quest reward from Tranquillien, it is only available to Horde players.

Source
This item is a reward from the Tranquillien quests Rotting Hearts and More Rotting Hearts which start with Magistrix Aminel in Tranquillien in Ghostlands. To complete these quests, you must turn the following items to Magistrix Aminel:
 * 10 Rotting Hearts