Final Battle -- The Fortress of Regrets
If you need healing or whatever, now is the time to get it. Then
go to the Mortuary and get the guard to let you in. If this doesn't work, just let someone kill you and you'll
wake up in the mortuary again.
The portal is in the same room where you started the game. Before you enter the portal, talk to Morte. Once you pass through the portal, your party will
be split up and Ignus or Vhailor will
even attack you if he's still with your party, dependent on your alignment.
At the fortress entrance, you'll be all alone. First go east and talk to Deionarra. Tell her that you have HER ring with you. She pumps it up to +3 to all saves, +3 to AC, and +3 AC vs Piercing (thanks Quizmati!).
Now go west through the door and waste the shadows if you can. On
the platform in the middle of the room is a machine. Pull the lever marked X. There are three other machines
just like it, so you have to pull all the levers.
Now a portal will open in one of the rooms, which takes you to the Trial of Impulse. This is where Ignus attacks you. Wax him up good. (note: if your character has an evil alignment, Vhailor will attack you instead)
There's a hidden goodie (sounding stone) in this room as well near coordinates X=1149, y=927. It has a message from the Practical Incarnation and also tells you where you can find a stash of supplies for the Nameless One at coordinates x=458, y=1247. (thanks Thomaslew!)
Then touch the crystal in the middle of the room and this will take you to the Maze of Reflections.
There you will find three incarnations of yourself (Good, Practical, and Paranoid), and you have to convince them
to join you. One is particulary tricky, and it depends on if you're character is capable of forcing him to merge or not. You need high Wisdom to force the Practical Incarnation into merging with you (other people have told me they did it with as low as 16 Wisdom and high Int). I talked to the good incarnation first, then used the Bronze Sphere to learn my true name and get 2,000,000 exp points (which i used to up my Wis and Int), and then talked to the other incarnations and merged with them as well.
Now Deionarra will appear
and you have to talk to her.
Good luck with the ending! They are all different, so there's no point in telling you more…