Uh, I got an integer overflow with the wizard.
I got so much experience on night 17 I got negative talents. I am now stuck on level one, unable to level up anymore in proceeding nights or learn any more talents.
I had echomancy, double exp ability and the proc ability on level perk. The ability on level perk has been rate limited and is now preventing the game from crashing, but the combination, along with aoe damage like frostnova, allowed a loop of leveling up multiple times, triggering frostnova and killing onscreen enemies, and also triggering double exp, wherein echomancy triggers it again, causing a burst of experience and level ups.
At least this time the error didn't crash the game and I still finished the run.