a wailing banshee  

Well, we wiped 2 times. Our problem was definitely positioning. You MUST keep the banshees off the stage and Mr. Rancor on the stage(and out of the organ). If not all hell will most likely break loose. Have someone spam BACK OFF if he enters the Organ and then repull out to the middle of the stage again. One strategy that comes to my mind is to have all your melee get behind the Organ in the corners while your MA/SA are building initial agro. Then when they attack they'll push him back out away from it. You might have to switch this a few times when he nears either end of the stage as he has quite a few hp to go through. Any pet that has a lot of push is not recommended for this reason(its a small stage).

I recommend making sure all your people know to push the banshee's AWAY from the stage. If mana sieve hits your casters too much you're done(poof, dead). Keep all casters on stage away from the banshee mana sieve.

The second time around we did manage to keep this banshee alive although not particularly in good health. I can therefore, neither confirm nor deny my earlier post about this being the key to the banshee respawn. It could be that any of the 3 could be kept alive. I know that the other 2 can definitely be killed safely though, as long as this one is kept alive.