Aquarium Limbo

The Aquarium Limbo is a recently discovered area found in a personalized test copy of Super Mario 64, sent to Electronic Gaming Monthly. It's an alternate version of the Secret Aquarium stage, located within the Internal Plexus of the castle. It has no air bubbles, nor coins, although bubbles Mario produces are still there. It also uses Big Boo's Haunt's background and darker lighting to simulate night time. Its music is a slower version of Dire Dire Docks.

When starting the level, a glitch causes the Textureless Mario Anomaly to happen, making some bubbles or fish turn black. This also makes dying crash the game. It's rumored dying in this level can also leave emotional effects, similar to Wet-Dry World, or the apparition's memory loss abilities

File:Aquarium Limbo LOST.ogg

Song used in the Aquarium Limbo stage.

Layout
The Aquarium Limbo is a replica of the Secret Aquarium. It retains its defining features, such as the box-like shape, windows, and aquatic decoration. Differences include the removal of all coins, including the red coins, as well as the Big Boo's Haunt skybox and darker lighting. The exit level feature also does not work. Due to the Textureless Mario Anomaly occurring at this level, dying crashes the game. Its music is a slower version of the underwater theme that loops right before the drum track starts.

Theorising
Not many theories have popped up about the actual course itself, only speculation on what it could be after the audio was leaked by an anonymous retired Electronic Gaming Monthly writer. Recently, however, the course has been found. The leading theory about the course is that drowning in the course leaves psychological effects similar to Wet-Dry World's negative emotional aura, or the Wario Apparition's short term memory loss.