Audum in Saman in the item shop wants you to destroy a cursed mask for a customer of his. This becomes available in the latter part of disc 4. Unfortunately the only place it can be destroyed is the Temple of Enlightenment. After he gives you the Enchanter's Mask go to the temple (this should be one of the last places you go before finishing the game) and make your way to the The Altar of Truth. You can place the mask on the altar after the boss fight. Return to Audum for your reward.