I'm al Level 81 Battle-Mage, and I have done every main and side quest in the game. 100% of all my skills are Level 100, and I am going to tell you what MY hardest boss fight is. Well, there's three of them. Two are Dragon Priests. One is not.
?Miraak, the First Dragonborn - This enemy has proved to be, in my opinion, the hardest enemy in Skyrim. His lightning attacks completely destroyed my health at Level 61. I made an estimate that his Lightning Spell can zap you health down to 0 in around 1.25-1.8 seconds. I admit I did not come with much shock resistance, mainly because I've seen the infamous sword of Miraak when I visited him earlier on, and I expected Miraak to be a melee type boss fight. But much to my surprise he used one of the most powerful spells in the game. I landed on the Summit of Apocrypha with 30 health potions. I came back to Solthstheim with 1 Extreme Health potion...
Another major problem with this fight is that he regenerates his health three times. Because Miraak is constantly destroying you with his seemingly limitless supply of magic. I ended up chugging down health potions like a depressed man who wanted to drown his sorrows in alcohol...
Miraak can also used a $@!# load of shouts in battle. His unreleting force alone can throw you across the Summit of Apocrypha. And that Cyclone shout, oh my. Take it from an expert at Skyrim, Miraak is the hardest it gets.
?Zahkrisos, High Dragon Priest - In many ways this fight is similar to Miraak. Except Zahkrisos' lightning spell IS EVEN FRIGGIN' STRONGER. Zakhrisos also summons Seekers in battle and Seekers just happen to be in my top 5 hardest enemies list...
The only reason I think this fight is slightly easier is that Zakhrisos does not regenerate his health. Also, Zakhrisos does not use Dragon shouts in battle, where as Miraak does, and frequently too.
Some people say Krosis is the hardest Dragon Priest. I say BULL-SHIT! Its easy to take out the Dragon before you take on Krosis. Not to mention, Krosis' attacks did much less damage to me than Zakhrisos did. And I fought Zakhrisos at a higher level with much better armour. My main tip for beating Zakhrisos is to A) Get a decent follower. I used Serana as she uses strong spells and is an essential character, thus she gets back up again. B) Use slow time against Zakhrisos. Its to my firm belief that Zakhrisos doesn't use spells against the Dragonborn when your at close range. Slow time allows you to close the distance and get some critical hits in.
Seriously though, Zakhrisos is a real pain in the ass to beat and his lightning spell is in my opinion, the best destruction spell in the game. And because Zakhrisos must be killed during the quest Lost Legacy, and the fact that the quest is vital in the Dragonborn DLC makes him one of the hardest fights in Skyrim.
?The Ebony Warrior - Its extremely rare to see someone who I've fought at Level 81 be perfectly capable of holding their own against me. At Level 81, I'm basically invincible. Yet the Ebony Warrior proved a great challenge, and I haven't faced a challenge since I fought Miraak.
Melee against this guy is insanely hard. His Reflect Bow perk made melee combat insanely difficult, and at Master I found myself getting spanked. But at my level I have an almost infinite supply of health potions, so it really did not matter.
But without potions, this guy would be friggin' impossible. His sword does devastating damage, and that Reflect Bow perk is just insanely annoying.
Runners up on the list were ; Azhidal, Morokei, Rahgot, Seekers, Spriggan Earth Mothers, Legendary Dragons. Not necessarily in that order.
So now, I'm gonna give my opinion on a few matters on this thread.
Firstly, the Frost Troll at High Hrothgar's steps was NOT hard. If you can't beat him, just find the Spell Tome : Firebolt or go to the College of Winterhold, become a member and buy it off of Faralda for a few Septims. Fire-bolt demolishes Frost Trolls and when they're low on health, go in for the kill.
Secondly, Red Eagle? Seriously? I refuse to answer that queurie.
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