Princess Peach's Castle/Peach's Bedroom

Peach’s Bedroom is an anomalous area in Princess Peach’s Castle found in some personalized copies of Super Mario 64, being the bedroom of Princess Peach, hence the name. Peach’s Bedroom has been described as a C-shaped room with several unique decorations and other anomalies, such as the anomalous Ice Spire level. It has commonly been reported to appear on the Fourth Floor of Princess Peach’s Castle, though can supposedly appear in several other locations.

Description
Peach's Bedroom has been described as a C-shaped room taking place somewhere in Princess Peach's Castle. It consistently contains several unique assets, such as a bed, a nightstand, often with a Nintendo 64 or picture frame of Mario, and a closet. Another common piece of decoration is the Princess Peach painting seen in other parts of Princess Peach's Castle, though a Mario painting not seen in the base game has been reported to appear as well.

Peach's Bedroom is reportedly accessed with a staircase leading up to the center part of the room, often found in the anomalous Fourth Floor, though has been reported in other areas such as the room where Bowser in the Sky is. Peach's Bedroom also reportedly requires a key to access, though the actual key is inconsistent and commonly anomalous.

The Princess' Secret Toybox
The Princess' Secret Toybox is an anomalous level reportedly found in part of Peach's Bedroom, accessed by jumping into a toybox somewhere in the room. It has been described as a large area filled with several children toys, such as a doll, often being of a character in the Super Mario Bros. franchise, or large building blocks. This level reportedly has a variety of different enemies from throughout the game, as well as unique enemies mimicking common toys.

The Ice Spire
The Ice Spire is another anomalous level reportedly accessed through Peach's Bedroom, though the method of entry is much more inconsistent than The Princess' Secret Toybox. It has been described as a tall tower made out of ice, using assets and enemies from Cool, Cool Mountain and Snowman's Land. It commonly requires the Wing Cap to traverse, with a Power Star at the top of the level.

Princess Peach Painting Level
Several levels associated with the painting of Princess Peach has been reported to be accessed in Peach's Bedroom, likely due to the Princess Peach painting commonly appearing in the area. However, the exact level has been inconsistent, due to several levels being associated with the Princess Peach painting, most commonly being the World of Dreams and/or the Sunken Castle.

Theorizing
Peach's Bedroom appears to be a remnant of the Fourth Floor that is reimplemented by the Personalization A.I. due to it's common manifestation alongside the floor, particularly being rather finished due to it's overall consistency throughout reports. However, this has caused some conflict with the association with the Fourth Floor, as a common theory is that the Fourth Floor is a large maze due to the floor being unfinished and reassembled by the Personalization A.I. through Dynamic Level Arrangement, meaning that Peach's Bedroom would logically lack much consistency if it was part of the Fourth Floor. However, this idea has been combatted with another theory that it was simply completed before the main floor, as another fairly consistent room, the Internal Garden, has also been reported in the Fourth Floor.