Hm. I haven't figured this out yet. I've read what you've all said, but my particular foray into the pit isn't bearing fruit. What I mean is, I'm unshackling the possessed PC and "parking" in next to the bony nuisances. They can't seem to hit anyone. Likewise, my own characters can't seem to hit my possessed character. I'm playing on Hard, but I tried bumping it up to Torment to see if they hit better. They do not.
What am I missing?
I also don't understand the concept of unshackling yourself and standing next to a skeleton to get hit. I don't see how that makes sense in an RPG sense. And since the game is rather elevated in terms of its RPG elements, that seems out of line.