Spawn locations for "poshadow.txt" map file (note for all Plane of Shadow named map locs, see this quest entry):
Every 30 seconds, buffs itself with "Power of Fear". Dispell this quickly because it AEs "Shards of Fear" if it fades naturally.
Volx Xi Xakra is also a part of the group mission "Breaking the Seal" (see this quest entry for details).