And because my post was moved to the ultra-ending thread, I'm gonna write it here again.
What if ToX had a special level with an enemy wielding Eptyron from CLIVAN? It's an artifact axe that softens material of whatever it strikes. This would have several positive effects:
a) ToX would have a completely unique threat; it needs special levels like GC, but with dangers and enemies distinct enough to make the dungeons feel different,
b) material softening is very cool mechanic, but wouldn't work on regular enemy because of frustration; on unique enemy, it would make him interesting and dangerous,
c) there would be an artifact axe which IVAN now sorely lacks.
Also, what about making one of the maze rooms a whole special maze floor floor instead? Just as GC has zombie level, ToX could have maze level. That would quite break the similar room-and-corridor level stereotype and hopefully make it a challenge with strong walls and several guaranteed strong enemies (like the dwarf on zombie level).