Princess Peach's Castle/Floor 2B

Floor 2B, with 2B meaning second basement, refers to an anomalous floor of Princess Peach's Castle added to the game via the Personalization A.I. Most copies of Super Mario 64 have only 3 floors and a basement, though a rare Fourth Floor can appear, and a Second Basement can also appear with similarly rare circumstances. This floor is much more similar to an actual floor than the 4th floor, with several unique rooms and levels.

Geography
The "main room" of Floor 2B remains relatively consistent to the first recorded screenshot of Floor 2B. 2 large hallways that can either lead to more rooms, the Flooded Hallway or the entrance, a raised platform that can have a door on it, a painting of Princess Peach, a sign on a wall, and a carpet. This main room can also have more doors that can lead to rooms containing more levels, or other rooms such as the Block Room.

Flooded Hallway
The Flooded Hallway is an area similarly to part of the first Basement that is filled with water. It usually allows access to another part of the floor with a level or two, though some have reported another section referred to as the Flooded Basement that is a large area filled with water, that strangely can appear similarly to the regular Basement. The Flooded Hallway reportedly appears in an old magazine that covered Super Mario 64, though this is unconfirmed.

Block Room
The Block Room is a room that is usually filled with several ! boxes of various sizes, and the painting for the Switch Dungeon level. The blocks usually do not have any items inside them, though some have been reported to contain items. Notably, the Switch Dungeon painting cannot be entered in some copies before all 3 cap switches are activated.

The Crawlspace
The Crawlspace is a small area that requires the player to crawl to traverse, usually accessed by crawling into a hole in a wall. It can consist of several paths to other parts of the floor, though some have reported a central room filled with several warp pipes, potentially meant to represent the castle's plumbing. Some have reported Skyhigh Pipelands can be accessed from this area, though this is uncommon.

Switch Dungeon
The Switch Dungeon is the first level attributed to Floor 2B, occasionally only accessible when all cap switches have been pressed. The level usually consists of 4 smaller levels requiring the use of all 3 caps, as well as Koopa shells or any anomalous cap, most commonly the Rainbow Cap or Starman. The first part of the level is usually a large box with a corresponding box color on each wall, with the doors on each wall leading to the trial with the cap corresponding to the color. The usual enemies in this level can be Thwomps and Chuckyas, though others have been reported. Each trial can give the player a star, and a 100 coin star has also been reported.

Boiling Hot Basalt
Boiling Hot Basalt is a lava level very similar to Lethal Lava Land, though has several differences. There is commonly no volcano, finished versions of Blarggs that can go through grate platforms which are usually present, and a large upper area where most Bullies in the level are present. Big Bullies have been reported, though Boss Blarggs have also been reported, as well as the unused Motos enemy.

Dry Bones Desert
Dry Bones Desert appears to be the Floor 2B equivalent of Shifting Sand Land, similarly to Boiling Hot Basalt and Lethal Lava Land. This level's defining features are reportedly the lack of a pyramid, instead having an outdoors temple, and the Dry Bones enemy mainly seen in Big Boo's Forest also being reported here. There is also usually less quicksand and a larger Tox Box area. The other reported enemies are Pokeys, Piranha Flowers, and Klepto. Notably, a screenshot of a Pokey in an earlier build of Super Mario 64 has been speculated to have actually been taken in Dry Bones Desert and not Shifting Sand Land.

Toxic Cavern
Toxic Cavern is a cave level similar to Hazy Maze Cave and/or Big Boo's Haunt that reportedly has a purple tint and an industrial aesthetic, with most areas representing parts of Big Boo's Haunt or the open areas of Hazy Maze Cave, with several death pits scattered throughout. The level's reported enemies are Boos, Scuttlebugs, Snufits, and supposedly a purple flame that attacks the player that appears to resemble this level's most common painting, a purple version of the Lethal Lava Land painting.

Bowser in the Randomized Realm
Bowser in the Randomized Realm is Floor 2B's most common Bowser level. It is unique in that it is entirely randomized and personalized by the A.I. based off of the player's inputs, hence the name. The level can use assets from anywhere in the game, similarly to Dynamic Level Arrangement, and in rarer instances can create entirely new assets. The level's difficulty is usually determined by lives lost and star count, as well as general difficulty increments implemented by the A.I. Bowser's dialogue also reportedly changes based on the difficulty. Bowser's key that he drops also reportedly does not unlock anything, though some reports state it can unlock new floors. The stars in this level are also inconsistent, though a red coin star is usually reported. It is theorized this level was a testing grounds for the Personalization A.I., before being scrapped when Nintendo decided to cover up the A.I., though the A.I. can bring the level back.

BlackJoystick's Documentation
Youtuber BlackJoystick has documented Floor 2B in several videos, alongside several levels they have accessed from it. In the description of the video, they say they accessed the floor with Big Boo's Key, and that none of the paintings were enterable. BlackJoystick begins in one of the 2 main hallways, enters the Block Room and then another room that appears to have the Boiling Hot Basalt painting. they then find the area leading to Bowser in the Randomized Realm, and then enter the Flooded Hallway before finding the Dry Bones Desert painting and an area that leads to Bob-omb Village. Their next videos document Bowser in the Randomized Realm and Bob-omb Village, with their final video documenting Floor 2B being in the Painting Room before documenting the Painting Creator anomaly, and Skyhigh Pipelands. It is not entirely known BlackJoystick will return to Floor 2B.

Greenio's Documentation
Youtuber Greenio has uploaded a video titled Promo Show documenting a cancelled news show called Nintendo Mania where Mario talks about video games. This video goes through several anomalies, such as a playable Luigi, before the player climbs part of Princess Peach's Castle, enters a window and then a pipe which warps them to Floor 2B. This version appears to have strange red and blue tinted walls and floors, and the raised platform's door is locked, requiring a key. The paintings in the main room are all standard paintings, except for what appears to be a real painting version of The Starry-Night Skies' painting. They then read a sign in the room, which says that this is the "secret floor". They enter a hallway that leads to a room with several paintings: Toxic Cavern's painting, a painting of Yoshi, a painting of a Pokey and Fly Guy, a painting of a Boo, the beta painting for Cool, Cool Mountain, and several paintings from the standard game. They then go back to the main room and enter another door, which has the sky texture seen in the painting for The Sun level as a real painting. They then enter the final hallway, which contains the path to the Flooded Hallway, as well as the Flooded Basement. Before entering the Flooded Hallway, they talk to a Toad, who says:

"I'd love to take a swim, but I'm scared of how deep this pool is. And that tunnel... I shudder just thinking about it! I wonder where it leads to... ?"

They then enter the Flooded Hallway, before eventually entering the Flooded Basement. Notably, the show's Mario reappears on the screen though doesn't say anything and instead stands still, looking very sad. The player traverses the Flooded Basement, which appears as a clone of the regular Basement, slowly losing health, before eventually drowning. The video then displays a distorted show Mario that is in several pieces while a voice plays in the background. The video then cuts to an image of the Eternal Star Statue, which doesn't have a plaque or star, before both slowly fade in. The video then ends.