LogFAQs > #980042254

Octopath Traveler. Technically it's post game, but it is the final boss that can only be fought after all eight of the possible bosses that earn you the credits sequence. It's an enormous jump in difficulty over everything else in the game and it's the only time you need all eight characters geared up at once and two separate, extremely capable teams. Even well equipped, it has every nasty trick in the book, hits like a train, and requires you to put out a lot of damage fast if you don't wanna get rekt.