When I first saw Rat Monarch in Labyrinth I got really afraid, with a flashback to a rather recent daily with another monster class in another maze-themed dungeon. A bad layout could easily doom the Rat. Fortunately, this was not a bad layout. Far from it.
With ENDISWAL and CYDSTEPP in the glyph pool the dungeon layout and high-damage boss were not the issues they could have been. Tomithy as the randomized boss is pretty much as easy as it gets (even Rat can just straight up fight that guy with no blackspace antics). Taurog, Mystera, and Dracul in the default deity loadout gives you plenty of options. And to top it off, a balanced dagger mere steps into the dungeon? Free momentum. Then you had stuff like Elven Boots, Badge of Courage, and Agnostic's Collar. There were more good items than I had cash to spend on them. Still took this one really slow and carefully (for me, anyways), but it really wasn't bad.