In order to complete the TzHaar Fight Caves, you will have to kill this huge monster. It attacks with melee, magic and ranged.
The best way to kill it is to avoid using melee on it, and instead range or mage him to the death while using protection from ranged/magic. If you get hit, it might hit up to 97 hitpoints at once. Although it is not dropped, you will be rewarded a Fire cape when it is killed.