I did this last, before heading to the hall of echoes, so was at a relatively high level (36) and didn't have too much trouble (it did take a couple restarts for me to get my technique refined a bit). I had my creature summoned, and stood a little in front of Zandalor, firing arrows at the creatures from the 2 front rifts (more to get their attention than do damage) and switched to melee when they got close, occasionally having to Rush Attack a memory eater from the rear rift.
