Im facing off Karstagg the ice giant king, this guy is redicuosly tough...he does mass damage hits, health and stamina sapping auros, and can summon ice wraiths. The first time ive truly had to go %100 force and use everything in my arsenal to try and take an enemy down and still havent yet, but 2 things that are very bothersome about him are that he can sometimes send you flying with a hit that sends you straight into the cave from the battleground area and when you return his health has been completely restored. The one other thing that is the most bothersome bug ive found in Skyrim for me is after he hits you like a rag doll and you eventually get back up off the ground his health has completely restored also!! I read nothing about him having regeneration powers like that. Has anyone else experienced this problem/bug also? If so let me know im not the only one, i appreciate the feedback!
Well the first of the two things you mentioned, him hitting you out of the area is just unfortunate, nothing you can really do about it.
The second, however, isn't actually a bug. Karrstag is classified as a troll, so he has health regen. If he doesn't take damage for a certain amount of time, he regens health, so by the time he knocks you over and you get back up, he's all topped off.
The only way to combat this is a). Don't let up the damage/don't get hit. Which is rather difficult.
Or b). To combat his health regen, set him on fire, fire does extra (significant) damage on trolls and karrstag and negates his health regen, giving you time to get back into the fight if you get knocked down. --- Close your eyes, cover your ears, listen. The world around you is not as it seems...