Ghost House level created by Procedural Generation.
Procedural Generation is an uncommon anomaly found in very few cartridges. This feature created by the Personalization A.I., lets the game pick from a select number of pre-determined rooms, to create a seemingly infinite stage. Procedural Generation is only accessible on Nintendo 64 consoles connected to the Nintendo 64 Expansion Pak peripheral.
The Ghost House[]
The only current recorded instance of Procedural Generation in real time, is a Ghost House level, and a video of it can be found here
The video starts off showing the Princess Peach's Castle map, in its pre-release form, with the player playing as Mario and starting off in a nearby pond. The HUD indicates that the version shown is The POWER Build / Early B-Roll Build or a build around that timeframe. The player runs off to the right of the grounds, where they are suddenly transported after walking next to a tree. The player emerges in the Ghost House. Several theories indicate that this level could be related to or is Hollow Horror Halls.
The other side of this door has never been documented, no matter what form it takes.
The player spawns on a platform, with a door on one side, and a slope with a door at the bottom on the other. The player decides to go down the slope. The other side of the door that was not chosen, has never been documented. However, Procedural Generation generates unique rooms each time, so it is very likely that every time you enter the stage, it is different.
The player proceeds through the door next to the slope, and enters a huge hall filled with Boo enemies, and a singular Mad Piano. Soon, the Boos overwhelm Mario, and he takes damage, revealing the build shown to be The POW Build.
Mario is maneuvered into another room, which contains a large bookshelf, and some more Boo enemies. After running around for a few seconds, the player discovers 2 Doors. Although they are not entered in this recording, they will have had random rooms behind each of them.
Mario wanders back into the previous hall, and the Mad Piano awakens. The player frantically jumps and runs out of the way but gets damaged in the process.
The player runs back to the door in which they came through originally and goes back to the slope. After running back up the slope, the player runs to the other door, but sadly, the footage cuts off before the other side can be seen.