Hi, agreed with what you said about Torment's superbness

I'm glad to see someone posting such a nice discussion topic - I've been lurking for ages, but felt like I had to sign up and contribute a little now
*Lots of spoilers below*
About Ignus and Vhailor - Did you not get the memory flash where you remember Ignus approaching one of TNO's previous incarnations (the one who taught him) as a young boy, trying to talk to him about his connection with fire, and the previous incarnation rebuffs him quite violently? (thrusting his hand into the flames in the fireplace, I think)
I believe that memory is the most direct information you get on TNO's history with Ignus. It's also one of my favourite "memories" in the game - the brief description of Ignus as he was when he was human, this frightened boy who is already obsessed, really added a lot of depth to his character for me
Vhailor was a relentless and powerful Mercykiller when alive, who persued TNO's practical incarnation all over the planes. Knowing that Vhailor was a potential threat even to him, the Practical incarnation cleverly trapped him in the room where you encounter him in the game. You can get a memory flash about this, but I forget the exact dialogue option that leads to it. I think it's when you ask him to judge you.
So, both Ignus and Vhailor have plenty of reason to hate TNO as he was responsible for destroying both of their lives as humans. Perhaps he was indirectly responsible in Ignus' case, but it's still strongly implied in that memory I mentioned before that Ignus' power could have manifested itself differently if TNO hadn't been such a violent teacher.
About Ravel as Mebbeth, Marta and Ei Vene - The way I saw it, Ravel doesn't physically become them in the sense where they exist as real, individual beings. Ravel is still mazed when you encounter her, and even though she says she can leave, it's obvious that she never left the maze physically before. That means that Mebbeth is not a shapeshifted Ravel in the flesh.
So either she takes temporary control of their minds, like a possession, or they aren't real people at all, but only images projected by Ravel, which is what I tend to think.
Because this is Planescape, it makes sense that Mebbeth would *feel* that she is a real person, although she is really only an illusion created by Ravel. That would also explain why she has only got a vague sense of how she could be both Ravel and Mebbeth at the same time.
Something which supports the illusion theory is that both Mebbeth and Ei Vene seem to be visible only to TNO and his party. When asking other Dustmen about Ei Vene they will say that they've never heard of her, and when you go to the market for Mebbeth someone comments that they've never heard of any midwife in Ragpicker's Square. That would lead you to believe that they aren't real, and didn't exist prior to their meeting with TNO.
One odd little thing is that Marta says that Pharod told her strip the items from the corpses. That would make it seem like she *has* had a life and interactions with the rest of the world prior to meeting TNO.
About the Practical incarnation - Like you said, the confusion must be due to timeline inconsistensies. Also (someone please correct me if I'm wrong) when Practical meets Deionarra he is preparing to travel to Baator (we learn that from Zachariah) presumably to question the Pillar of Skulls. This would mean that he is visiting the Pillar for the first time and has not got Morte with him yet, making the timeline even more messed up.
The First incarnations crime - I've played the game enough times to be sure that there is no way to find out what his crime was. I imagine the story writers left this out for the same reason they you never learn his real name: No matter what they told us, we would probably be slightly disappointed. Imagination is sometimes better than fact

This is pure fantasizing, but in the public sensorium there is a sensory stone which contains the experience of a war general who has burned a whole city full of innocents because he had orders to do so, and he experiences an overwhelming sense of regret. I always liked to interpret that line you get that "This has stirred some faintly familiar memory in you" (or something to that effect) to mean that perhaps the First incarnation's terrible crime was something similar to this.
There are a lot of hints scattered around that the First incarnation *was* involved in the Blood War somehow, as I'm sure you've noticed. Probably his crime was connected to that.
On character closure and the Fortress of Regrets - I think it depends on your own actions what precisely happens to Deionarra at the end. If you tell her that you don't love her and that Practical was only using her, she says that she will finally go to rest, as she remained only for you. If you say that you do love her, I agree with Fable that she remains a ghost for you.
As for the others, I don't really have any idea what they would do, but I like to think that Annah would find the opportunity to begin a better life. I think that having been exposed to TNO's dilemma of identity would have made all his companions think more about their own, and deal with them in ways they couldn't before. Also, her life in the Hive was uprooted with Pharod's death, so she has very little to go back to. I agree with you that it would be nice to have more closure on this, as I don't really see her ending up very happy, although she may have changed for the better. She had just learned what it meant to love someone, and then lost him.
I think Morte would enjoy finally having his freedom - I'm not sure I see him joining Grace on a potential quest to search for TNO. He was his friend, yes, but he had also suffered along with him for so long, and Morte's general views on life taken into account, I think he would want a life without any more torment.
I would guess that the Fortress collapses some time after TNO and his companions leave it, as it was sustained by his own regret and by his mortality only.
I hope it's okay to make such a long post - I guess it makes me look a bit obsessive seeing as how this is my very first post
