Just standing next to the Ebony warrior triggers a scripted event that causes you die automatically. He is actually very weak and underpowered compared to a true nord. I placed all my stats in Health for except 20 levels, that equals 61 levels of health. I also have smithing at 200 and armor at legendary with upgraded weapons. When I first met him he is fighting a frost troll and doesn't attack but stands there. Turns out you have to be the aggressor and trigger a fight. Upon commencing the fight I collapsed and instantly died, he didn't even have to do a thing. I reloaded my save and the same thing happened again. This time i attacked him and backed up and noticed he wasn't doing much damage to my character to justify an instant death. I blew him off the mountain and fought him at the bottom where I instantly died again. I reloaded and tried it again but hit him and backed up and hit him and backed up. I fought for about 5 minutes, his attacks are weak and his armor is vanilla compared to my superior gear. I have double enchantments for health and stamina in the +150 range for regen. In conclusion the Ebony Warrior has a trigger (that goes off when fighting to close) that I'm guessing is similar to Ebony Mail armor, but instead of causing poison over time you simply collapse and die. I'm sure someone in a fight could easily misinterpret the event as a powerful hit or spell and fail to realize the game is triggering an instant kill victory for the Ebony Warrior.