First of all, I made it to the bottom of the Castle of the Winds 2 dungeon. On the 24th level, I ran into a weirdness where if I picked up this specific belt from the floor, my game would shit the bed and I could no longer save or save-as. Similarly, on level 25 I ran into another one of those, but I don’t know what caused it.
Level 25 is the last level of the game, and is where the game’s boss “Surtur” lives. In this particular game, it’s pretty easy to aggro the other mobs with him and pull them into a hallway for slaughter. Surtur himself is difficult, not that he hit particularly hard (all of his attacks are elemental, so you just cast all of the resist spells; except for wind, but whatever), he just has a shitload of hitpoints and has a really rude way of teleporting before you can get your last hit. If you can catch him quickly you can finish him off, but waiting even more than a few turns he will start healing himself.
I chased him around a bit today and I couldn’t get him, so I decided to take a break. The strategy is get full of mana and health, put on all the resists and shield, then approach him somewhere that is not line-of-sight for a door or a hall (other mobs will wander across you and you’ll have to fight them too), then fight him. Keep fighting and healing (he seems resistant to elemental, you can use magic missile if you really want) until he is just about dead, then he will teleport. If you are lucky, you can teleport to close enough to where he is to shoot him with something. Otherwise, look at your map (detect monsters on) and figure out where he is.
I chose to keep using teleport for this as it is cheap and only takes one turn, lessening the chance that he will heal. I was not able to get him this time, but am pretty sure I can get him on the next battle. You dirty bastard.