yeah all you really need to do is make sure you dont equip skills where he can heal himself and you will most likely win. i kept all my warrior skills and just put enchantments that were not helpful to him and i killed him before i even looked at the clock. Easily under 5 seconds.
Not sure if this actually worked, but I brought reg sword skills, heal area, frenzy and flurry. I used Flurry, but I swear mirror used Frenzy. Went down in less than 5 seconds.