Kuwabara is now more sensible. He doesn't shout as much and he's more calm about things. A big difference from the last time we saw him. Also, his awareness has made him popular.
Hiei is the only one that wasn't at the reunion. His sister also never found out who he really was.
After the past three years, while Yusuke and company have been to Demon World, Keiko's short hair has now grown long.
Edit: Kurama is mistaken for Kuwabara's girlfriend by a few of Kuwabara's female friends. When Kuwabara tells them Kurama is male, they think that Kurama is Kuwabara's boyfriend instead. The implication of homosexuality was completely removed in the edited version.
As Keiko is walking with her friends, a large trunk passes them with the word 'Narlboro' written on it. This is most likely a reference to the cigarette company, "Marlboro".
In the scene at Mukuro's fortress where all the men on the patrol duty are walking, one of the men pronounces Mukuro's name wrong.
If you own the DVD and turn on the English subtitles, you can see at the very end of the episode when Smile Bomb is playing that the word 'strength' is spelled wrong.
When they show Kuwabara's reflection in the window of the train, if you pause at the right moment, you can see a sign outside of the train that says in very scribbly yellow letters 'Yu Yu Hakusho end'.
At the end of this episode, instead of playing Daydream Generation, the full version of Smile Bomb is played.
At the very end, they show a white backround and in black letters: "FOREVER FORNEVER". This could be a typo meaning either, forever forever or forever for never.
This is the only episode where multiple characters do the preview for the next episode. Yusuke, Botan, Kurama and Kuwabara all have a line or two in the preview.
At the beginning of the episode, the marks on Yusuke's body begin to fade, probably due to his spirit energy overpowering his demon energy. However, when Yusuke is shown farther away, his marks are still clearly there. Then, as the fight continues, his marks disappear completely.
Near the end of the episode, you discover that Koenma had Botan package all of the footage from Yusuke's adventures as a spirit detective, with his assistant, Jorge, as the narrator. This compilation is the entire series of Yu Yu Hakusho.
In this episode, it shows that Yusuke can fire his Spirit Gun well more than 5 times, which was his usual limit.
In the preview for the next episode, the title for it is shown. This is one of only two episodes to have this happen, the other being episode 52; "The Death of Genkai".
Apparently, Mukuro happens to be more powerful than the power of the Dragon of the Darkness Flame.
Response: Not necessarily. After the attack goes through, Mukuro states that while Hiei could never consciously control the dragon, it does "feed off the intentions of his soul". Hiei later goes on to say that Mukuro can now "leave her hatred in the past where it belongs" as she realizes her shackles are breaking from the aftermath of the attack. Who's to say that Hiei, a man once constantly haunted by his own dark past, didn't put just enough energy into that attack in order to express those feelings towards Mukuro?
In this episode, Kurama uses a version of his Petals and Thorns technique. However, instead of using it has a defense, like against Karasu, he uses them offensively.
The Okunenju Root Kurama used in his fight with Shigure was planted by Yoko Kurama hundreds of years before the fight ever started.
Kurama's Rose Whip is broken by Shigure's Ox-Bone Sword in this episode, even though it has been said many times that Kurama's Rose Whip can cut through any substance.
The fight between Kurama and Shigure is not shown in the manga, but it obviously did not turn out like the anime fight did, as Shigure appears later in the last book of the manga, and he's alive.