There is an NPC in a camp with a few others. Killing them all leaves one invincible and determined NPC. His name is Gonnar Oath-Giver, the Stormcloak commander. I found him in Rift Stormcloak Camp north of Treva's Watch and across the river on the East side of Nilheim. His blows are considerably weak. I was at level 64(armor rated at 200ish).
Pick a fight with him with your back to a rock corner, rig the controller to keep your block up and he'll wail on you for skyrim days. He's quick too and seems to have infinite stamina. As I write this, I've leveled twice.
I've seen some other horrible bugs in the game, for instance, don't give your unique weapons to your stay at home wife Ysolda or try and put them on the display case or weapon holder in your house at Solitude. I lost my Chillrend and Dawnbreaker.
I've got a dozen briar hearts stuck in my inventory after completing a quest for one.
I'm also unable to figure out why my White Phial isn't filling any more.
And I read that the spell to 'summon unbound dremora' is used only once to put a Daedroth atop the College of Winterhold.
Coulda been funnier than a frenzied chicken.
Bottom line: Skyrim is an Awesome game