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Only drops if the player has  Argent Dawn Commission,  Rune of the Dawn /  Seal of the Dawn, or (pre-3.0.2)  Mark of the Champion /  Mark of the Champion equipped.

If you lost or destroyed your trinket, you can speak to Argent Quartermaster Hasana (H) or Argent Officer Pureheart (A) to receive a replacement.

Corruptor's Scourgestone no longer has a use since the system for gaining reputation with the Argent Dawn was changed for Cataclysm. Its item quality is Uncommon because it was worth significantly more reputation points with Argent Dawn than the Common-type lesser scourgestones.