When fighting The Fire Warrior of Lesarkus u need to use IceArrows collected in Dungeon.

Please be aware that Forums Walkthrough for this Quest states only one IceArrow needs to be collected, and that other arrows can be used as long as one IceArrow is used.

From my experience u will recieve a message similar to this if u use one IceArrow and switch to others:

"You must use IceArrows to Defeat The Fire Warrior of Lesarkus."