Bit of a weird behaviour from him today. I nuked the living daylights out of him and he came to visit me on the ledge. Ended up taking 3 swings from him, blinked 2, stoneskin absorbed half of the 3rd. Eventually I ran out of mana and manafont wore off, so I scurried off to a corner to rest, out of AoE range.
I rebuffed myself with blink/stoneskin and sat down thinking I'd stand up when he came to kill me and pop off 1-2 nukes. Only...he never came. Everyone but me died and he returned to his spawn.