Quest 76

Requirements: In order to complete this quest, you must know the Thief skill "Half-Inch". It is the top skill in the Thief tree and allows you to steal from enemies. The Proof of Thief is an accessory that gives a chance to automatically steal from a defeated enemy when you are victorious in a fight.
 * Head to Gatara and visit Budecho in his house at G-6. He lives in the square near the well.
 * You'll need to stop Gasmon, but you have to do it in a certain manner.
 * While wearing the Mask de Mucho, we must steal Gasmon's heart, and then defeat him.
 * Getting the mask is simple. Across the street from the tavern is an armor shop. The Mugger's Mask is the only accessory in the Armor shop, priced at 1200 gold. Purchase it.
 * Put on the mask and then head back to Goble Desert East. This time, enter the Sand Cave in the middle of the map. (D-5)
 * Stealing his heart is pretty easy, but the fight is against a triplet of Gasmons that can paralyze.
 * Prepare yourself and defeat the boss after stealing the heart.
 * Return to Gatara and visit Budecho to complete the quest and claim your reward, the proof of Thief!

Completed Summary - You've defeated Gasmon as requested by Budecho, who lives in a house near a well in the mountain city of Gatara. You were recognized as the King of Thieves by Budecho.