Shadow King
Grand master of the Order of Talos.
draugr death lords are the hardest for me even more so than dragons.
Has GOT to be slaughterfish. When they aggro on you, your companion and horse both try to kill it, but what's worse is that you can't just go and kill them, because you can't use weapons or magic in water.
And now you've got Ataxia, a condition which will be promptly forgotten because you rarely check Active Effects in the Magic Menu. Good thing the people of Skyrim can give you an expert diagnosis. Yes, I am sick. Thank you.