This is a formal reminder that we are still playing a Mario game.
Chapter 6 is not exactly a proper Chapter- the entire story, from start to finish, sets up both the expectation and the delivery that we are going to see the end of a world, a nice way to ensure that the stakes of the story- largely forgettable since we stopped visiting Ancients- have been reinforced. Chapters 3 through 5 are all about their respective settings, with the Void being easy to block out of the sky by the prevalence of interiors and Chapter 4's background. In some ways, the fact that Chapter 6 is going to raise the stakes does colour the story- the Duel of 100 would not be a satisfying chapter if played straight. Instead, the fact you are challenged to complete a fraction of the Duel of 100 is to escalate the anxiety in the player, making them feel like their time is being wasted while disaster descends upon the world they are currently occupying.
King Sammer, and the Mimi duplicate taking him over, presents an interesting use of Mimi compared to her earlier appearance in Chapter 2 and her later one in Chapter 8- even despite her childish temperament and refusal to properly adjust to the face she wears, the fact King Sammer himself is fairly childish and nobody comments on his unusual behaviour means that she passed by completely unnoticed until the penny dropped. By being set in feudal aesthetic Japan, the audience expectation is that the story will be about honourable samurai who follow their ruler, and it turns out that was exactly the wrong move. It seems kind of a shame that the Sammer Guys never really get the chance to reflect on how they managed to let her slip by.
Meanwhile, the World of Nothing is... well, they say "there is no greater fear than imagination", but when it comes to destruction, that adage proves somewhat incapable. Players may be excellent at imagining a place as it collapses, but they are far less good at seeing the remnants of what stood before it. Seeing the World of Nothing- a single flat line dotted with only the occasional Sammer remnant- is a simple statement: This is what being erased looks like. When Count Bleck says he wants to erase all worlds, he truly means that there will be nothing left. Not even ruins. If his promise to his minions of creating new worlds on top of where the old worlds once were was true, then these Worlds of Nothing would be overwritten like old save files to do so. And somehow, despite everything, the game is fully prepared to make this worse.
Mechanically, Chapter 6 sucks. Not only is there a Flipside and a Flopside Pit of 100 Trials, but there's a Duel of 100 as well? In addition to potentially exhausting the player on 100-floor challenges, the Duel of 100 is a far inferior version of the Pit of 100 Trials as well. Each battle is preceded by entering a door, doing a somewhat awkward jump onto a platform, going through preamble, and then starting the fight. This fight will last approximately five seconds before you fade out into a postamble, and then have to walk over to the other door- and then the hop off the platform can get just as awkward. The Pit of 100 Trials understands how to make the idea of a 100 floor dungeon in a platformer work far better, and while the Duel of 100 has some decent jokes and references to make of it, 100 was far too many to make an impact and a lot of them get obscure enough it's hard to pick them out from the original ones. Add that on top of the World of Nothing being a clear "the story impact is all that matters, and the gameplay being terrible is part of the point" sort of area, and it's hard to like playing Chapter 6. At least it's the most memorable one, because of both the Sammer Guys and the World of Nothing. You can't deny story is the selling point here.
