*Grumbles and flings a pillow at Myst* Not 'minion!'
*Coughs* Anyway, I beat it at level 41 or so on about the third try. I've been speccing a 2-hander and resto staff since the beginning because I found out that DW had very few skills that I'd want to use, which makes balancing your magicka-to-stamina useage tough and I was always running out of magicka way too fast, and I can basically substitute a couple of the NB abilities for ones that I have on my 2-hander, which is handy.
Basically what I'd do is I'd wail on Mannimarco with my 2-hander hard the first round before he summons his ghosty things, knowing he was about to bring them out because of my npc dialogue, swap to my resto staff, drop a Circle of Protection in the middle of the room and hit Expert Hunter (both fighter's guild), swap back to my 2-hander and kite the ghosts around in a circle inside my Circle of Protection until they were dead, using almost exclusively Funnel Health (yay self heals!).
After that phase, I'd go back to SLOWLY beating on Mannimarco using left click and the disrupt right click then left click for his health drain attack. To get around the big red circle of death, I basically just kept circle strafing around Mannimarco. The key to getting out of those, whether you're ranged or melee, is movement. If you're standing still and it's dropped on your face, a dodge roll isn't enough to get you out of range of it, but if you're already moving, you won't have to have that split second reaction time to start moving out of it before you roll. Anyway, so as you're strafing, the left clicking is JUST to get your magicka and stamina back up, since the summon phase of this fight is very intensive. I tossed in a few Funnel Healths between those phases because my health was getting lower, but you NEED your magicka and stamina to kill and dodge the ghosts.
Last notes, 1) I've been saying I keep needing to pick up a full set of heavy armor (I've been running medium), and actually had it on me for that fight, so I put it on beforehand. 2) I've been keeping a ton of extra skill points (looking at my screen right now, I have 13 unused skill points) so that if anything at all comes up, I can just get a new ability that it seems that I may need. 3) I'm stupid and completely forgot about my ultimate ability, so that will probably help you out quite a bit. :P 4) If you're ranged, you can be totally cheesy and line of sight Mannimarco around the outer pillars (unless he's doing his channeled ability that you need to disrupt; that one goes through the pillars), and shoot him a couple times, then when he moves to get you in sight, move to another and repeat; dunno how well this works for his summoned adds though.
Hope this works, good luck and happy hunting!