Princess Peach's Castle/Castle Dungeon

The Castle Dungeon of Princess Peach's Castle is a small anomalous area reportedly found in the Basement behind a star door that supposedly only appears to experienced players. The Castle Dungeon has been described as having a similar appearance to the Basement of Princess Peach's Castle, and contains several unique levels.

Description
The Castle Dungeon is typically described as being made up of very few rooms, though is relatively consistent in overall design, likely due to it's small layout and likely being scrapped at the last second. The first room is the most consistent, being made up of a hallway leading to a painting and a jail cell containing another level, and a doorway to the rest of the Castle Dungeon, which is much less consistent though typically contains another painting and some other rooms, such as another room with a jail cell containing some coins.

Fox Forest
Fox Forest is a forest level that has been compared to Big Boo's Forest and is characterized by it's unique Yap enemy, a fox enemy that hides in bushes and jumps out and attempts to attack the player when the player goes near the bushes containing a Yap. Fox Forest has been described as a dark forest supposedly with unique warps at the end of the level that warps the player to the other end seamlessly, giving off the illusion that the level is endless. Fox Forest's enemies (excluding the aforementioned Yaps) tend to include Goombas and Spindrifts.

The stars reported in Fox Forest tend to be found inside of trees, some of which have sub-areas with similar designs to Tick Tock Clock that must be traversed, occasionally including the red coin star. Other stars that have been reported include finding 5 secrets, rummaging inside of a bush, defeating a unique boss fight against an Ent (a living tree), and bringing a box to a rabbit character resembling MIPS the Rabbit, potentially being a remnant from when MIPS the Rabbit had a bigger role in Super Mario 64.

Bully Beach
Bully Beach, as the name suggests, takes place on a level mainly populated with Bullies, who are reportedly defeated by being knocked into the water or a unique hot spring hazard, being a unique trait for Bullies not seen anywhere else, though the level can contain other enemies such as Goombas, Bubs, and Skeeters. The level is divided into two main segments: the beach, and the ocean area that takes place underwater.

The Power Stars reportedly located in Bully Beach are most commonly found by defeating a Big Bully, using the Metal Cap to obtain a Power Star inside a current similarly to the Through the Jet Stream mission in Jolly Roger Bay, defeating all the Bullies in the level, obtaining a star in an underwater maze, obtaining 8 red coins, finding a Power Star hidden in a coral reef, and finding a treasure chest containing a Power Star similarly to the chests seen in Jolly Roger Bay and Dire, Dire Docks.

The Cremini System
Main Article: The Cremini System

The Cremini System is a late-game space level typically found by unlocking the cage in the main hallway of the Castle Dungeon. It has been described as an expansive space area with several sub-areas taking place on several areas such as planets and asteroids, with the main area taking place in space acting as a mini hub world for the sub-areas that make up a majority of the level. The planets on this level are very varied and inconsistent, meaning that a majority of the level's geography is unique in each report.

Bob's Documentation
Bob is a Youtuber who documented the Castle Dungeon in a video of the same name. The video begins with Bob entering the entrance to Vanish Cap Under the Moat, instead popping up in the Castle Dungeon by falling out of a hole in the ceiling. The layout of the Castle Dungeon sticks to the most common layout though notably, the painting that commonly depicts a fox is replaced with a painting of Bowser, and the jail cell that commonly contains the Cremini System is hidden from view, implying it does not exist in the copy. A unique room that is not typically reported in the Castle Dungeon is found towards the end of the video, consisting of a table and several Bowser paintings adorning the walls. Bob enters a door in this room and the video ends.