How come I just knew Radek would have the results of an elaborate experiment ready for me?
Thank you both. I had always suspected it might be so. Of course I have also tried to fight Anephas, Kol, the Spirit of Xydusa, etc. It was my experience that it was impossible to hit them. (It would usually give the sound of a parried blow and I would get messages such as [my character] misses or [NPC] parries). I have not tried fighting Kol in Erathmedor's lair, but Kerah is the only NPC I have been able to hurt, but only up until a certain point. Since it seems like Cet charges one with a quest (killing Kerah) I had always hoped it would be another official (fourth) way to end the game.