Defeat the bosses at the end of the penultimate dungeon blindfolded! This includes the setup before the fights. This would be around 2:50:00 into the run, so quite close to the end.
Upgrade the category to New Game Minus. This game mode disables leveling up and forces characters to stay on their lowest possible level, adding an extra layer of difficulty. This would need to be set at the start of the run, it's not possible to change game mode mid-run.