Peach's Castle (ピーチ城上空, Pīchi-jō jōkū, Above Peach's Castle) from the Super Mario 64 is Mario & Luigi's home stage in Super Smash Bros. It does not return in Super Smash Bros. Melee. In 1P Game, the player fights a Mario and Luigi team on this stage.
 In competitive play
This stage is considered legal in tournament play as sole counterpick stage in Smash 64, though only in the USBR64 ruleset. While it is a counterpick, it is rarely played due to the prevalence of Dream Land and Hyrule Castle, though it is an occasional counterpick by Donkey Kong, Mario, and Yoshi mains, especially against Link players. The stage is labeled a counterpick due to the inability to grab ledges (allowing some characters to be edgeguarded or gimped much more easily than usual), the bumper hazard, and the angled platforms on the top left and right of the stage, which prevents some KOs and is a disadvantage for characters who prefer to KO in that direction. It is is banned in the Japanese ruleset for similar reasons. It is also a rarely used doubles stage, due to the somewhat small size and stage hazards. There are some tournaments which instead ban this stage in doubles and prefer to use Saffron City.
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. These platforms are very easy to DI off of as well. 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 difficult for most characters to recover on this stage since the two floating platforms limit recovery to the top platform and there are no ledges that can be grabbed, with the the moving black platform on the bottom of the stage greatly aiding recovery, but it isn't always on the side the player is on).
This stage's elements come from Super Mario 64. The stage takes place in the sky above Peach's Castle; in the background, it can be seen 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 moves 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.