There is a hidden quest available in Solstheim that can neither be found in journals nor a specific waypoint.
This quest allows you to confront a legendary creature known as King Karstaag, a large, powerful frost giant that was one of the last bosses in Bloodmoon. He lived in a large ice fortress on the island, but that fortress is all ruins now.
This guide will help you find and finish the quest, which also unlocks the Bloodmoon Easter Egg. In addition to the exciting encounter with this beast, you will also get a bonus ability, provided you defeat him.
Don’t Underestimate Him
Giants are generally tough to take down; their hits send you flying off. Thankfully, good armor and high levels will aid you in these situations, but just ‘good’ won’t get you anywhere you want to be when battling against the King of all frost giants.
Karstaag is a big meanie – he’ll whack you so hard you’ll think you are an aircraft cruising at high altitudes. Because of that, you’ll need the best equipment and items Skyrim can get you. Those Level 81 players would ask ‘is he tougher than the Ebony Warrior?’
Well, that really depends on your play style, but Karstaag seems to have superiority to the Ebony Warrior because of his size and the amount of volume he occupies. So, unless you have some really badass melee weapons, armor, and shouts, you won’t have an easy time. I highly suggest getting all three words of the Dragon Aspect shout before attempting to battle the giant.
How to Find and Initiate the Quest
There is a cave in the northern part of Solstheim, called the ‘Glacial Cave’. Head there; if you’re having difficulty, it is west of the Benkongerike Cave. Go inside this Glacial Cave, and you will find a unique item there called ‘Karstaag’s Skull’. Interesting, eh?
Grab the skull, and head west, and then a bit south to find the Castle Karstaag Ruins, a place located in the northeastern part of Solstheim. Once you’re inside the ruins, place the skull on top of the throne there, and King Karstaag will appear for a battle.
As stated before, Karstaag has some very damaging melee attacks. But that’s not the only thing that is bothersome; the giant has a constant ice aura around himself that saps you of stamina and health – not a good combination!
Another very irritating this is that the entire place will shake during the battle. This can really get your aimed magical attacks to go off target, so it’s better to rely on shouts (Dragon Aspect and Yol combo!) and your melee attacks.
Once you do enough damage, the King of Frost Giants will start playing unfair, and will summon Ice Wraiths to aid him. Fend of the wraiths and attack him, or ignore them and just keep on throwing everything you got at the King – that choice is yours to make, and really depends on your gear and your style of play.
Once you defeat him, you will gain a ridiculously overpowered ability ‘Summon Karstaag’. What it does is self-explanatory, but such power comes with some limits; Summon Karstaag can only be used 3 times in total!
If you haven’t fought the Ebony Warrior yet, I suggest using it once on him. Good luck!