Karstaag is a powerful ghost frost giant found in Castle Karstaag Ruins. In 3E 427, Karstaag ruled over the Riekling tribe in Castle Karstaag. During the events of The Elder Scrolls III: Bloodmoon, he was slain by the Nerevarine, but his ghost can be summoned with his skull.
Karstaag can be fought as part of the unmarked quest "Summoning Karstaag." It requires traveling to Glacial Cave and retrieving his skull. Once it has been obtained from the cave, it must be taken to Castle Karstaag Ruins, which can be unlocked on a Master level, or traveling through the Castle Karstaag Caverns, and placed upon his throne. Several rieklings have taken up residence in the ruins, and must be defeated first.
Once the skull is placed on the throne, the ruins will rumble and begin to shake. A spectral Karstaag will appear from the throne and immediately attack. Once he has been defeated, he will vanish, leaving only his ghostly remains.
As a reward for defeating Karstaag, the power Summon Karstaag will be granted, which allows the Dragonborn to summon the beast to aid them in battle. This power is unique in that it can only be used three times, after which it is no longer available.
Karstaag is a powerful foe and can prove to be quite a challenge, making him one of the hardest bosses in the game. He attacks much like a regular Frost Giant, using his club, fists and stomp attack, however, these inflict much greater damage. His stomp attack is so strong that it can throw the Dragonborn across the room, much like an Unrelenting Force shout.
He also has a permanent frost cloak with a large radius that inflicts frost damage, the severity of which is dependent upon game difficulty. Occasionally during Karstaag's stomp attack, a blizzard will begin to swirl in the courtyard, inflicting additional damage to health and stamina over time, which itself can be fatal. Because of this, some form of frost or magic resistance is useful, especially as stamina can be depleted within seconds.
Karstaag is completely immune to frost damage, poison and paralysis, however he does have a slight weakness to fire damage. Once he begins to take damage, he summons three Ice Wraiths to aid him in battle, if given the chance. He also regenerates health very quickly. During the entire battle, the ground will shake violently, much like when staggered.
One can counter Karstaag's high health regeneration and armor by using all three words of the Marked for Death shout. With repeated use, the effects stack and will greatly reduce his armor value and his maximum health. This will reduce his health regeneration as well as add a damage boost due to the negative armor value caused by the shout. Using the Blessing of Talos and an Amulet of Talos to reduce the shout's cooldown is also recommended. Karstaag's stomp attack knocks away any follower the player may have during the battle, with the only exception being the Ash Guardian and Storm Atronach. Due to Karstaag's 75% resistance to shock damage, it is recommended to summon Ash Guardians during the battle, so it is important to have a number of heart stones at hand. It is also recommended to acquire the Companion's Insight perk to stop the Dragonborn accidentally hurting or killing the followers.
- Full force Unrelenting Force
- Wabbajack's instant kill
- Mehrunes' Razor's instant kill
- Any form of enchantment
- "Agra Kul!"
- "Agra Vel!"