SPOILERS BELOW!!
Pierrot Le Fou is best categorized as an episode that is remembered for its style, mood, and action sequences rather than its plot. I feel that's a constant theme in the top episodes of Cowboy Bebop, but it's also expected. There's only one true continuous plot while most storylines are episodic. However, the great thing about Bebop is that it takes advantage of the space setting while mixing it in with genres you wouldn't think mesh with sci fi. Jazz, mystery, and humor all blend well within the world of the Bebop Crew.
As I said before, Pierrot Le Fou is very minimal on plot. Mad Pierrot is an unstoppable hitman, Spike walks in on one of his hits, they have a fight and Spike survives, now Pierrot is on a vendetta to kill him. There's also some backstory for Pierrot about how he came to be so unstoppable (the standard sci-fi staple of "experiments") and how it caused his mind to regress to that of a child. But all that jazz isn't really that important.
What is important is how unstoppable Pierrot is. He's probably the best fighter in Bebop, giving Spike a run for his money. I could even see Pierrot wiping the floor with Vicious. No one comes close to his unstoppable-ness. He can float in the air, is an expert with firearms, and even with his obese appearance, he's as agile as a cat. In fact, throughout all their fights, Spike doesn't even land one hit on him (except for the end).
He's also the scariest of the Bebop bad guys. Bebop isn't really that heavy on horror, but if I had to categorize this episode, it's certainly the scariest. A look into Mad Pierrot's face, and you get chills. The hollow eyes paired up with that eerie smile rocks you to the core. He's the perfect enemy for this kind of episode. And they have their fight in a Disneyland type rip off, which just adds to his devious child-like killer persona.
I praise the episode's well animated fight sequences, but this one is all about mood. There's a minimal soundtrack. No catchy jazz riffs here. Instead, you're treated to the background noise of a "it's a small world" like carnival song as Spike literally fights for his life at an amusement park. It's the perfect juxtaposition for his battle. On one hand, he's essentially fighting someone with the mentality of a child, on the other he's taking on one of his blood thirstiest opponents.
And spoiler alert, Pierrot dies. But it's the way that he dies that is so unsettling. He cries for his mommy, the truest display of lost innocence, only to be crushed by a giant furry robot that he probably loves. However, you feel exhausted after the fight is over. Spike has gotten his ass kicked, twice. Usually, Spike offers a moment of recollection in the end, but this time, he's disgusted at the messed up situation and what humans are possible of doing. As he best puts it, "just forget about it".
