Ice Troll King

The Ice Troll King is the boss monster for the quest The Fremennik Isles. He is presumably the leader of the ice trolls. He is located on the northern part of the isles. He uses all 3 combat styles, which includes a Range attack where he throws rocks at you, a Magic attack that freezes you, and a mighty Melee attack that hits hard and sends you flying. Note that he only uses it if you use the prayer Protect from Melee.

How to commit Troll Regicide
The main thing to be careful about is that he attacks using his melee attack that knock you backwards. You MUST use the Protect from Missiles Prayer. It's best to keep that prayer on since when you use Protect from Ranged, it negates it's attack which knocks you back. Wear the Yak hide armour and Fremennik shield (created during the quest). This, combined with the Protect from Missiles Prayer, should keep your damage to a minimum.

Magic is not suggested against the Ice Troll King, even Fire spells. The Ice Troll King is, obviously, a Troll, so he has good defence against Magic and Range attacks - this means that Melee is recommended. Yak hide armour should be worn although. The best way to kill the Troll King is to use Protect from Missiles prayer. If this prayer is used, the Troll King can only used magic and close-range ttacks, and you can negate it's attack which knocks you backwards. After the Ice Troll King is dead,decapitate it and take its head to the Burgher to show you have defeated him.

For further detail on other parts of the quest, see The Fremennik Isles quest guide.