I descented 15 floor of dungeon and explored it completely, but hadn't found Dredmor anywhere. I checked the whole floor 4 or 5 times, he's just absent. I'm playing with both two expansion, Steam version of game.
Most likly he spawen within a secrect room which is seperated by breakable walls. This sometimes happens. The only way to make sur eis either use the cheat ode and uncover the map or try to break the dungeonfloor itself with bolts of mass destruction ^^
Actually, it's possible to break said breakable walls with pretty much any area of effect attack, and on the last floor it's difficult not to have access to any. The only question is, do you know where to look for the breakable walls?
You're right, he had spawned in the tiny room, and entrance was blocked by the furnace. Thanks to the Arcane Capacitor skill, it was easy to find it.
