Located in the upper reaches of Princess Peach's castle, this is one of the most compact battle zones in the game. Beware of the bumper above the castle, because it can bruise even the biggest brawlers. A small constantly moving platform at the base of the structure makes this small arena even more treacherous. With four players fighting simultaneously, things can quickly get too close for comfort.
Peach's Castle has two main platforms, one on top of another. It is possible to fall through the top platform. The bottom platform partially comprises a block going left to right. On the top two corners there are two floating, inward-angled platforms that prevent people from being smashed away too easily. It has a floating Bumper on the middle above the second platform of the stage. This bumper moves slightly left and right (it remains stationary on 1P Mode though). It is harder to recover from this stage since the two floating platforms limit recovery to the top platform and there are no ledges, aside the moving brick platform on the bottom of the stage which isn't always on the side the player is on.
In Smash 64, according to the American ruleset, Peach's Castle is usually considered a counterpick. This is because of the inability to grab the edges, meaning that some characters can be gimped or edgeguarded much easier than usual, and the Bumper hazard and angled platforms on the side of the stage that can prevent KO moves that would have otherwise KO'd. However, the Bumper can be used for various unique combos, and can also be used by characters such as Pikachu to escape pressure. The stage is often counterpicked by Jigglypuff and Kirby players, and the lack of edges that can be grabbed serves as a disadvantage to characters such as Link and Captain Falcon. In the Japanese ruleset, the stage is banned as with every other stage except for Dream Land, due to the reasons mentioned above. It is also occasionally banned in doubles tournaments, due to the listed reasons along with the fact that the stage is too small.
This stage's elements come from Super Mario 64. The stage takes place somewhere in the sky above Peach's Castle, hence the fact that, in the background, one can see that Peach's Castle is very far below the actual stage. The sign seen on the lower level is also from the game, and the bridges likely are inspired by the broken bridges seen in the Cool, Cool Mountain course. The triangular-pyramidal platforms seen on the upper sides of the stage resemble the ones seen in stages with dangerous ground, like Lethal Lava Land, which move around in accordance to Mario's placing. Unlike said platforms, these ones do not move at all, let alone are not activated by weight.
The music is a remixed version of the original Super Mario Bros. theme. It can also be heard in Melee during the cutscene in Adventure Mode before the fight with Luigi, though the track is absent in the Sound Test.
Peach's Castle official art.
Peach's Castle in Super Smash Bros in Training Mode.