Oh, just a note, it is possible for a single warlock to take the full duration of Netherspite’s blue beam. Dot him up and then use Drain Life. The added +spell allows you to get more life back than you’re losing to the increased shadow damage. Occasional heals help.
Also.. um.. be careful on the timing of you Curse of Doom. If you put it up late.. and it goes off just after he returns from his nether phase.. but before there’s anyone in the red beam.. he will so come and eat you.. and he pays no attention to Soul Shatter.. and everyone -will- yell at you for pulling him totally across the room and out of the proper placement for beams (so totally not (entirely) my fault).