I've thought about doing multiple BHs, but the ground targeting spells (Death from above, etc.) have kept me from it so far. I just got one of those on my Sage last night and if he's not the character in control, it's virtually impossible to use it (or at least I can't find a way). I can't imagine trying to control 4 characters with those type of spells. But if you figured out a way, I bet it would be amazing damage.