What is the best way to defeat dragon preist Krosis?
Solution 1:
Krosis is one of the few masked dragon priests you'll meet outdoors. In fact, its not just outdoors but conveniently located on top of a mountain.
Thus, the easiest method of beating him would be to simply Fus Ro Dah him off the top of said mountain.
If you want to do it the 'normal' way, you'll have to bring ample fire resistance as he has a staff of fireball. He is also weak to fire so brining along a staff of fireball yourself or have ample fire magic would greatly help. Distracting him with summons (like the flame atronach) is a good idea as well.