So, I've never heard of Karstaag until yesterday. I was like, lets do this on my level 89 character! So I got his skull and placed it on the throne. Before he appeared I thought, "I'm going to kill him on legendary." He appeared and instantly my health dropped from 600 to 150 in about 3 seconds. I drank a potion of ultimate health, hit him once, and I had to drink another one. Safe to say, that fight lasted 30 seconds. He completely destroyed me. In my professional opinion I say he's impossible to kill on legendary. Well, not impossible, but very, very, very hard. Has anyone done it on legendary, without cheating?

Well I can tell you he's pretty darn hard to kill on Master difficulty, heheh...
Finally got him, but I died a half-dozen times.

Now that the Restoration Potion exploit is corrected on PC (by USKP), Legendary difficulty is like the answer to a question no one has asked, y'know?
But I guess if you level your guy high enough, and Master's not doing it for you any more, then be my guest.
Using Duel-Combat realism, Master is hard enough for me! It's plenty nasty.

You'll get advice to "summon Dremora Lords".
Seeing Karstaag one-shot them as fast as I could summon them, I realized that's not going to help too much.
(those advice-givers have obviously not fought Karstaag themselves.)
He's bad!

I put it on adept difficulty and he nearly killed me 3 times. If it wasn't for Dragon Aspect and the dude that comes out and fights for you when you get hurt really badly, I would've died.

Afraid I'm not familiar with him.

So, right now, I'm fighting him on expert difficulty and the attack that sends you flying? Yeah, he sent me outside of the his cave with it. But I came back in, the battle had restarted, and power attacked him. He did his attack again and I went flying up hit, hit the top of the mountain having 1 health left and I drank a potion. I went back in there fought, used stormcall and killed him. Trying it on master now!

Well then...

It has been posted that there is a way to get upon the ledge behind the throne and use it as a platform from which to snipe ol' Kars. Using magic or bow from such a perch would keep you from being Dovacicle.

He just sent me out of the map...

I actually just sent my 360 save to PC, and I plan on spawning him, the Ebony Warrior, Miraak, and Alduin, adding them to the same faction, and fighting them all at once on legendary. That's the plan, anyway.

I heard Karstaag was pretty tough, so I prepared. Even at Master (pretty looped out, Alchemy, Enchanting, Smithing), his destroyed me. Took my 20 potions of Ultimate Healing. I used everything I had. All Black Book rewards, Maker Stone powers, vanilla powers, Sanguine Rose, and a follower. It was ultimately me who took him down.

Most enjoyable fight I've ever had. Well done Bethesda.

Can someone point out(on a map of possible) where this Kaarstag is? I'm horrible with remembering names like this in TES and don't know if I have encountered him yet....thanx.

He's a part of the Dragonborn DLC as a hidden boss. You go Glacial Cave on Solstheim and grab his skull. Head to Karstaag Ruins fight your way to the courtyard. Place the skull and the throne and step back.

Ahhh, I downloaded DB but have yet to play it. Thanks for the replies.

I had Dragon Aspect active with Serana distracting him part of the time. Dragon Warrior appeared just seconds before the last blow. I'm not sure if it was me or him that ultimately put him down. A close and titanic battle to be sure and worth the price of the DLC to me. I thought it would be a cakewalk with my uber OP character (Without exploits).