ToME: the Tales of Maj'Eyal

First and formost, I almost have no clue what is going on so I may have to trouble explaining this. When I got down to the last floor I saw the boss no issue. Hit him for a while and got him down to 80% or something like that. Then he teleported and now he seems to be completely invisible. Seems to be an oozemancer since he has slime trails and an anorthril because he sets glyphs but he also seems to have shadows and can cast creeping darkness as well so does that mean he has 3 classes? The bosses name is Belalle the Ancient Lich. I've been trying to find this thing for hundreds of turns now and I still, ever since he teleported, have not seen even the slightest glimpse of the thing even though he is still hitting me for arcane damage and such. Is this a bug or am I majorly missing something here?

The monster type Ancient Lich gets access to Anorithil stuff and Creeping Darkness and Shadows. They're horrible monsters even when they're not unique bosses.

You got really unlucky.

Plan A. At a time when you've just been hit, so assume he's nearby, try right-clicking each square - sometimes (or always, dunno) you get the option 'Inspect Creature' and that tells you where he is. It'll be slow to play with just that method though.

Plan B. If you've arcane eye, rearrange your recent generic points if necessary to get it to the 'mark a monster' level - one visit to Plan A, from which mark the lich and then you'll see the eye move around.

Plan C. Give up (probably) on the farportals, by recalling - staying alive for the few dozen turns remains an issue.