Note: This quest does not appear in your journal.
After traveling to the ruins of Castle Karstaag, there are two ways to reach the courtyard: You can either pick the master-level lock on the front gate, or take the long route through the Castle Karstaag Caverns, a large Riekling cave. The cave crisscrosses the main cavern multiple times and there are Rieklings on every level.
Once you get to the courtyard, you will see a large throne. Place the skull here. Be prepared for a very difficult fight. Once you place the skull, back up. Karstaag will appear as a ghostly frost giant with horns and a permanent ice cloak. When he appears he will cause a massive explosion of ice that looks like a blizzard which will hang around a while and take up a large area. Karstaag fights like a regular giant but hits a lot harder. He can summon three ice wraiths at any time in the fight and he can do it multiple times. He is a very powerful foe and can kill poorly-equipped characters rapidly.
- It is possible to summon Karstaag, leave using the front door, and then climb over the ice wall (just to the right of the door, while looking at the door) to strike at him from above. He and his summons will not be able to strike the player while standing on the ice above. Karstaag will move towards the door in pursuit of the player but he never actually exits, making him an easy long distance target. Player summons and companions will still attempt to fight Karstaag on ground level.
- It's possible for Karstaag to knock back the player into the Castle Karstaag Caverns resetting the fight, and thus his health.
- All of the quest stages are empty: 0, 10, 20, 30, 240, 250, 255.