Kolodion is the wizard at Mage Bank. You will have to defeat him to finish Mage Arena III. He goes through 6 phases all of who attack with mage:
1 - 100hp 2 - 150hp 3 - 200 hp 4 - 200hp 5 - 400hp 6 Chaos Elemental - 750hp
After you beat him for the quest you are able to challenge him as many times as you'd like to farm runes.