AKA "the Experiment". As the adds stop you using beneficial spells as a healer (and those that cure arcane whether purchased or not) are beneficial), and attacking spells as a fighter, a healer/fighter duo makes this easy. Fury ideal with SK or Pally. Fury does the attacking and fighter does the healing. Weird and stupid. Of course those with excellent armour can probably wait until arcane wears out and can cast attacking spells again. Ordinary fighters need cure arcane (purchased), even easier for them if they have a healer in tow
Think the single adds are on a timer, at least 6 - 10 (or more!) spawned during the fight with my pally. Adds didn't do as much damage as I expected but boss didn't seem to drop in health if I didn't switch. There was enough time between each to kill the add get a few of hits on the boss before starting on the new add. Was a long fight thanks to poor DPS, but easy even if the time it took was depressing. Used Perrin merc, as other mercs such as SK needed rehiring.