Oligar will at times "face" a groupmember (red text). This person must joust away sideways, the group must stay out of line-of-sight between the two and not be in front of him (he will turn towards the person).
at ~70% 3 statues will pop. Kill the right one first (memwipe until down!), then the center statue (might remove a stoneskin effect?).
Do not kill all 3 statues, i.e. leave the left one up or they'll instantly respawn, he is killable with the right and center ones dead, not sure about other combinations.
DPS Oligar until (either you or him) are defeated.