The final boss has approximately 89k. On a level 70 35 hagi/hsta 1300+ AC paladin, his max hit was 510 and he hit 36% (for the short time he was alive).
The "A Horrifying Vision" hits in the mid 600's max (ave around 200 - 400), he flurrys too. The Spider Illusion it casts is a DoT / Root, it's slaped on who ever has agro and he casts it more then once, however the effect is short lived. A Horrifying Vision dispells buffs, I lost four. It summons aswell, other wise you could kite it. A Horrifying Vision is slowable, snareable, ect. We noticed no resists. One groupable at lvl 65. I tanked him with a good cleric at lvl 64 with only 5.5k hp. Don't expect much of a reward, other then satifaction, and Saryn Tower Key info.
We did him with one group (levels 62-67), but wiped the first attempt at 17% because he resisted slow twice and then killed the chanter and got a couple of big flurries in on our tank (who also only had about 5.5k hit points, with 8k or so he wouldn't have died).
On the second attempt slow landed the second time and then he was easy. Dropped a Paladin-only neck item that doesn't seem to be on the list: forget the name, but it was AC12 with a few stats.
"Don't expect much of a reward, other then satifaction, and Saryn Tower Key info."
Well, we got better XP fighting through the Shadows to him and then killing him than we did in our camp in the zone outside :)
Killed this guy with one group... dropped a nice set of Necro Legs and a War/Pal/Shd Lance. Was rough with one group... would suggest you bring backup.