Princess Peach's Castle/Floor 2B

Floor 2B refers to an unfinished floor of Princess Peach's Castle that adds itself to the game via the A.I. Most copies of Super Mario 64 depict the castle with only three floors alongside a basement, with the rare chance of a fourth floor occurring. However, this one can also appear, with just as rare circumstances. To access this floor, you have to also have Big Boo's Forest unlocked. After beating Big Boo, a key will unlock the door to this new floor. The floor consists of a sunset themed wall texture, and rooms slightly larger than normal. Various paintings, including paintings of skyboxes, and paintings of previous levels. The only new painting is a purple version of Lethal Lava Land's painting. Floor 2B looks a little bit different in each copy that has it.

Flooded Hallway
The Flooded Hallway refers to a part of Floor 2B that is filled with water. Swimming across it brings you to another part of the floor. It has a wall preventing you from trying to go above the water, and has a bottom part to swim through. The part of Floor 2B the hallway brings you to has Dry Bones Desert, and Toxic Cavern's painting, as well as other miscellaneous paintings. Flooded Hallway has also been rumored to been seen on an old magazine.

Block Room
The Block Room is a room filled with huge versions of the ! Blocks, with the Switch Dungeon's painting on the wall. The blocks act as platforms and do not have any sort of items inside. If the respective switch has not been pressed however, these giant ! Blocks become transparent like their normal counterparts. The corresponding color of the painting also turns grey if the right switch has not been pressed, meaning you can't go through it.

Switch Dungeon
Switch Dungeon is a level only accessible in Floor 2B when all switches have been pressed. The level consists of 4 trials based off of the caps, the Wing Cap, Metal Cap, Vanish Cap, and unused Rainbow Cap. You start in a box with each side colored with the corresponding ! Block, and a door. Entering a door takes you to one of the trials, and completing one of the trials gets you a star. There are also a variety of enemies such as Thwomps and Chuckyas to act as obstacles. Some geometry, mainly in the Wing Cap trial, is also made to help with the difficulty. Switch Dungeon also has a 100 coin star that is possible to get on any separate trial.

Boiling Hot Basalt
Boiling Hot Basalt is a clone level of Lethal Lava Land, sharing it's theme like Dire, Dire Docks does with Jolly Roger Bay. The volcano has been removed, and some level geometry has been changed, including a finished version of Blarggs that can go through grate platforms. There is also an upper area unlike Lethal Lava Land, where you can find a majority of the Bullies in the level. There is also a boss, replacing Big Bully, called Boss Blargg. Boss Blargg shoots fireballs around his platform and has circling fire around him in the second fight. Kicking or punching him enough times kills him. The level also has a chance to showcase the unused Motos enemy as well, replacing the first Boss Blargg fight if called in.

Dry Bones Desert
Dry Bones Desert is a clone level of Shifting Sand Land. It uses Shifting Sand Land as a base, but the pyramid is now replaced with an outdoors temple of sorts. It also uses the same Dry Bones from Big Boo's Forest. There is less quicksand use, but the Tox Box part is now on another corner, and much bigger. The outdoor temple houses and oasis with Piranha Plants inside to shoot fire at you, like in Tiny-Huge Island. The remaining areas are usually pieces of slightly decorated desert, with Pokeys and Dry Bones scattered about. Klepto is in this level as well, still being able to steal the player's hat.

Toxic Cavern
Toxic Cavern is a course similar to Hazy Maze Cave or Big Boo's Haunt, but is set entirely underground. Most of the course is similar to the open areas of Hazy Maze Cave, with a purple tint and industrial aesthetic. There are also parts of the course structured like Big Boo's Haunt, but the industrial aesthetic is still retained. Multiple Boos and Scuttlebugs are scattered about the course, with Snufits inhabiting the smaller areas. A purple flame obstacle similar to the one shown in the painting is seen moving in a horizontal circle. The course also features multiple death pits, similar to Hazy Maze Cave.

Bowser in the Randomized Realm
Bowser in the Randomized Realm is a Bowser course, like Bowser in the Dark World or Bowser in the Sky. When entering the course, the game calls in the A.I to "randomize" the level like the title says. It uses assets from other levels, but can also use assets from the title screen and Peach's Castle. The level's difficulty is also determined by star count and lives lost, with the difficulty also affecting Bowser's dialogue. On less challenging versions, Bowser's dialogue will mock you, but for more harder ones, he acts frustrated. Forms of the stage with a more intermediate difficulty results in more basic Bowser text however. Defeating him gives you a key, but it can't be used anywhere. The stars of the level are completely different on each playthrough as well.

It's theorized this level was a test level for the A.I's capabilities before it was put into copies of Super Mario 64, hence why everything is randomized. Why it is still playable in the level is unknown.