The Sun Mage is an arcane-celestial caster with Fire, Sun, Radiance, Wildfire, and... Phantasm. With my regular talents, I could do nothing against these creatures that (even with resistance penetration) could chew up all of my damage and spit it out as healing.
My strategy was to lure each one of them out alone, equip the Spectral Blade (with no weapon combat talents, mind you) and whack away and away, hoping for a series of timely Silences to shut down all oncoming heals and damage shields. I had to initiate combat with each one of them dozens of times before I could defeat it.
Of course, the sensible, roguelike-wizened approach would have been to drag them to a far corner of the level and walk on by, taking the stairs to the next level. I guess I'm too easily excited by a thorny combat situation like this one
