We ran the final session last night, due to scheduling issues next week. This session is an utter drag. The first part is fine-- a skill thing, some gargoyles, ok.
It's when Kazit Gul shows up that it becomes painful. Kazit Gul is a save-or-die trap that can fly. He barely does damage, so everything the party owns to mitigate damage is not so useful. The party would have to do 160 hit points in non-save damage to defeat this guy-- very difficult to do in the one round before the killed PC's body disintegrates into dust (dust means no resurrection). The saving throw isn't too bad, for a Wisdom-heavy party (mine was very Wis-heavy), except that one unlucky die roll means death to one or more PCs.
We ran three tables last night. One of them TPKed and the players did not have fun. Part of that is probably the GM-- I'm going to ask him and the players today what happened. Part of it is simply "save or die" is a terrible thing to do to a party, even when they're facing the uber-lich of liches.
At table #2, the party defeated Kazit Gul and joined my table to finish off the 2 aspects there (table #3 came over to us). I believe the GM at that table probably pulled punches; he has a tendency to do so.
At my table, the party defeated the first gargoyles, and then Kazit Gul showed up and killed their monk in round #1.
This is where I cheated. The monk had made a deal with Baazka in session #1 to "die last," and Baazka wasn't going to let some upstart lich steal his kill. I scribbled down the stats for a pit fiend on an index card, and gave it to the monk's player and told him "your motivation is to get the monk's soul from Kazit Gul." He wasn't exactly an ally to the party, and didn't care about friendly fire, but the player was able to stay in the game and have fun.
Even with a pit fiend throwing fireballs as an at-will spell, the party lost their druid to the trap-the-soul (though that was from the other aspect from Table #3), and needed the help of Table #2's party to finish up.
The problem with Trap The Soul is that it isn't fun. There is nothing you or anyone can do once you're trapped to mitigate it--there's no saving throw. There's no remove curse. There's nothing except grind down a monster who is immune or resitant or avoidant of all damage types. The player is removed from the game. This can happen early on in the session, making players angry and frustrated and not causing a fun experience for anyone.
My advice: When you run this fight, next week or whenever, try to think of creative ways the PCs can undo Trap the Soul. Can a called shot take out a gemstone and release the soul? Can remove curse work? Resurrection? If they continue to focus on the phylacteries and destroy those and the gargoyles, will Kazit Gul relinquish the soul? Can you summon an angry devil (that one's probably only story-appropriate for my group, but maybe one of their other monstrous allies would show up for this showdown)?