Princess Peach's Castle/Rec Room

The Rec Room is an alleged unused room found in Super Mario 64. This room is found replacing the entrance to The Princess's Secret Slide in Super Mario 64 DS, where various minigames can be played. However, numerous players claim the Rec Room can be found in certain personalized copies of the original N64 release.

Overview (64 DS)
The DS Rec Room is a small, colorful area containing tons of toys and a shelf, alongside a painting on the wall which leads the player to Sunshine Isles, an exclusive stage to 64 DS. In the middle of the room is a lone Toad, who allows the player to play various minigames similar to that of New Super Mario Bros. There is also a star door to another room, containing entrances to play as the other characters, alongside the entrance to the secret slide.

Overview (Personalized N64)
The Rec Room in certain personalized copies of the N64 release is said to be located in a special door next to the room containing the secret slide. It requires at least 5 stars to enter. Inside the room is a large area containing tons of shelfs, pipes, and toads. The walls are covered in pink patterns resembling that of Peach's crown, and the floor is covered in Mario and Luigi's hat emblems. Along the sides of the room are small desks where Toads are found, who allow the player to play various minigames. Near a corner of the room is also a green Toad, who allows the player to play the multiplayer game mode The New Mario Bros.

Slide Speeders
Talking to the Toad near the bottom left of the room allows the player to play a minigame called 'Slide Speeders.' In this mode, the player is tasked to slide down a slide as quickly as possible, getting timed for how fast they reach the end, similar to the secret slide. The slide's visuals differs between copies, having different patterns, textures, and even skyboxes. This may be a case of the A.I randomizing the slide to give more or less of a challenge depending on how the player plays the game

Koopa the Quick
Talking to the Toad near the middle left of the room allows the player to play the minigame 'Koopa the Quick.' As the name implies, the player is tasked to race against Koopa the Quick across various stages found in the game, even those the player hasn't unlocked yet. This counts for every single stage, even those which are extremely small, (Cavern of the Metal Cap, Bowser in the Dark World, etc.) have little land (Rainbow Ride, Dire, Dire Docks, etc.) or even unused/personalized stages (Delicious Cake, Goomba Courtyard, etc.)

Despite this, however, Koopa the Quick always seems to have an exact pattern across every stage in the game, and even tends to walk on water/above air in order to reach the flagpole, which is always in the same location, located near the center of the course on top of a solid object. This could possible be done by the A.I to keep things fair.

Bowser's Rush
Talking to the Toad near the top left of the room allows the player to play the minigame 'Bowser's Rush.' The minigame takes place in an area known as 'Bowser's Arena,' which is a large arena surrounded by lava, as well as a few bridges and doors. Upon entering the area, the player receives a message from Bowser.

'' 'Mwah hah hah! Looks like you're out of luck,''

''Mario! You may have had a good time jumping''

and punching my troops, but there is no way

''you can handle ALL OF THEM! Mwah hah hah!''

Break a leg plumber boy, and I'm being literal!'

Afterwords, a siren plays as wave after wave of enemies begin swarming the arena. These range from simple Goombas and Bob-ombs, to more difficult enemies such as Chuckyas and Bullies, and even unused enemies, such as Motos or Blargg. Seemingly unbeatable enemies, such as Chain Chomps and Mad Pianos, also come into the arena. Around the arena are several boxes that dispense Wing, Vanish, and Metal caps as well as Koopa Shells to use to plow through enemies. With the Metal Cap, it can also be used to defeat previously unbeatable enemies such as Mad Pianos or Amps. Every 10 rounds, a boss comes into the arena, being any of the main bosses throughout the main game, or even some of the Alternative Bosses. Every 50 waves, Bowser also comes into the arena, in which he can be defeated by throwing him into the lava 3 times.

Big Boo's Maze
By talking to the bottom right Toad, the player can access the minigame 'Big Boo's Maze.' When starting, the player is warped to the outside of a large mansion as a Boo talks to them.

'' 'Eeheehee.. welcome, plumber, to my''

''mansion! Good luck finding your way''

''out of this labyrinth! Spoiler alert:''

you can't!'

The player is then guided to inside the mansion, where they enter a large, confusing maze filled with coins and Boos. The objective of the minigame is to explore the maze as further as possible while collecting as many coins as possible before being killed by the Boos. The deeper into the maze the player goes, the more dangerous it gets, as falling platforms, Mad Pianos, and water starts appearing across the maze. It is speculated that this was a test for Dynamic Level Rearrangement that was implemented into the Rec Room for unknown reasons, though this is unconfirmed.

Wet-Dry Dive
Talking to the Toad near the middle right of the Rec Room allows the player to play the minigame 'Wet-Dry Dive.' After starting the minigame, the player is warped to a large ocean with tons of icebergs in the background, as well as the skybox for Wet-Dry World. The player is instructed to swim as deep into the ocean as possible. In order to avoid drowning, the player must constantly collect nearby coins to replenish their air, which soon become more and more spread out and scarce the deeper the player gets. Enemies such as Bub and Unagi are also found in the ocean to hinder the player. It is unknown how the game or A.I manages to have an endless ocean depths, though it is possible it could be warping the player back to the top of the ocean with altered objects similar to that of the Endless Staircase, though this is unconfirmed, as the player is unable to go upwards while in the minigame.

Rainbow Flight
By talking to the Toad at the top right of the Rec Room, the player is allowed to play a minigame titled 'Rainbow Flight.' They are warped to an area similar to the Tower of the Wing Cap stage, although which much taller towers and a Wing Cap box in the middle of the ground. The player is instructed to fly as high up as possible without touching the ground. This is done by using various twisters similar to those seen in Shifting Sand Land to go further and further upwards, as well as flying through hoops to gain altitude. Strangely, the flight physics in the minigame as noticeably different compared to in the main game, in where the Wing Cap controls were mainly used for horizontal flight, the Wing Cap is noticeably better as flying vertically. This could possibly be done to make the minigame work. Like Wet Dry Dive, it is unknown how the game manages to have an endless sky, though the same theories apply to Wet Dry Dive.

Trivia

 * Interestingly, each of the minigames seem to be based on an existing course in the main game
 * Slide Speeders is seemingly based on the Secret Slide.
 * Koopa the Quick takes place in every stage in the game.
 * Bowser's Rush's skybox and lava makes it similar to Lethal Lava Land, though it has the music for the Bowser stages.
 * Big Boo's Maze is obviously based on Big Boo's Haunt
 * Wet-Dry Dive seems to be a mixture of Wet-Dry World and Dire, Dire Docks
 * Rainbow Flight is seemingly a mixture of Tower of the Wing Cap and Rainbow Ride, given it's title.