I completed this as a Nightblade at Lv 45......it isn't easy but it is doable. It is important to heal as much as you can. Potions when low or when you fail to dodge his AoE attack, and keep your other heal abilities active at all other times. I had 3 heal abilities, the one in the Siphon tree and the one from the Mage Guild tree and the Blood Well morphed for extra health regen from the Undaunted tree. Save your AoE and ultimate for when the adds come out. Move out of his AoE and I took him down with mostly basic bow attacks saving stamina for rolling out of the AoE and using magicka to keep the self heals going.

One of the inevitable problems a flexible class/build system like ESO has is that fight design becomes impossible, in that there are so many possible builds with a pitifully small selection (5) of available skills that some will find it too easy .. and some to the forums complaining as usual, see the QQ over Doshia from the 'pros' .. while other find it nigh on impossible .. see Doshia from the ordinary players' POV.

Seems this fight is a great example, slot the RIGHT skills .. and pray to God you've unlocked them and morphed them .. and it's hard but dobable, not have the 'rights' skill set for the fight and suffer.

The really bad part of this is that unlike other games where you have a far wider selection of skills available simply based on level, the skill is discovering how to use the skills to deal with the encounter, in a game like ESO it's very easy to run up against a brick wall because you haven't unlocked the set the fight designer requires you to have.

Self healing is a must.

A ranged interrupt will help you. You need to stop that life suck channel. Make sure you interrupt it quickly each time.

Dodge out of his AoE's. If you see a red ring remember: red means dead.

Don't blow your resources on him. Its a long fight. My suggestion would be to use Siphoning Strikes or either morph (Leeching will be best for your health though) and Haste. Then just do lots and lots of light attacks (assume you're using a bow.) When he channels his life suck, use the Poison Arrow morph that interrupts him. The other ability you'll probably want is Swallow Soul (Strife morphs) since it will whittle him down and heal you well as well.

You'll also need some kind of AoE to take care of the additional mobs he spawns. I'd suggest Impulse if you use destro-staff. Volley could work too if you use Bow. Or Whirling Blades if you use Dual Wield.

So its basically a fight where you just do lots of base attacks, use your abilities to Heal, Interrupt, and take out adds. Its intended to be long, so don't try to burst him. Be patient and keep yourself alive (health potions would also be nice.)

Also remember that Fire will be extra effective against the Undead. If you need a fire Enchant then whisper me in game @NordJitsu. Free of charge.

Also I havn't leveled a destro or heath staff, only two handed weapon, although i DIDN'T realize that the poison arrow interrupts his life steal, that will make things easier. I really dont wanna have to reroll my whole character because they cant't balance a boss like that for all players. if its not balanced it should at least be grouppable.