Grab the adds, dps the boss, repeat the same in 3 rooms, he ports around a bit.
The floor has 2 colored quadrants (blue and red) and accordingly colored glass-tubes with fluid.
Fight the boss at the quadrant where he stands first. When one set of tubes runs out of colored fluid, move to the other quadrant.
You should be able to finish him here. if not, watch the tubes and move him back to his starting position.
The tubes slowly refill, so if you don't have good dps you will have to move between the 2 ever faster...
Oligar of the Dead
Oligar will at times "face" a groupmember (red text). This person must joust away, group must stay out of line-of-sight between the two (he will turn towards the person).
at ~70% 3 statues will pop. Kill the right one first (memwipe until down!), then the center statue (dunno why).
dps Oligar until defeated (he or you).
Once you teleport into his tower, don't move. He has big aggro range, wait for your group to be ready.
During this fight (dunno when exactly) one group member will get a non-curable elemental detriment from Drinal, this person HAS TO MOVE AWAY FROM THE GROUP until it fades away, or it will start a chain of massive AOEs and Power Drains
Step on the lift, and take him down to 50%, but make sure your big-hitting DPS is ready for later! the lift will then ascend to the top - unleash hell now!
On top of the tower, directly target the boss, and make sure tank grabs all adds that may pop
Get out of red circles and cones!
INTERRUPT DISSOLVING SPIRIT! It's a death-touch instant kill.
Sometimes he does a nasty power-leech AOE (temporal Soulleech?) - good to have some tinkered Manastones etc. handy for that.
Don't know anything else, probably cure stuff. feel free to update and expand this info! thanks