If it's your turn to take on Yagluth you will most likely have a look on youtube to see how others are killing him, I did this too and took on a variety of methods mostly using frost arrows, fire potion and frostners, one youtuber even built a pit to drag yagluth in and limit his fire breath attacks, me and a friend tried all these methods and failed, infact just using frost arrows amounted to over an hour also using countless health and stamina potions and we still couldn't beat the guy.
We were beaten so many times that in the end I went back to watch the same videos, this is when I noticed something important that I think most people have missed, Yagluth himself causes hardly any damage when you stand right next to him, about -17 which if you have had fire potion and good food is nothing to lose, even weirder, meteors fly straight over your head and he doesn't use his fire breath.
We put this theory to the test and it worked very well, it took yagluth down in about 4 minutes and I took hardly any damage, I used one minor stamina potion and one fire potion, I didn't need any food as he went down that quickly, it sounds crazy but the Yagluth secret is to get as close as you can, I stood in front of his head without moving through out all the attacks, killed him and came out with full heath.
Yagluths entire defence is built around people running behind rocks and shooting from distance, stand right next to him, anywhere, and he's a ♥♥♥♥♥ cat, hope this helps some one