Super Mario 64/July 29th 1995 build

The July 29th 1995 build of Super Mario 64, most commonly known as the 1995/07/29 build, is an anomalous and mysterious build of the game. It dates back to before the Ultra 64 (the original name for the Nintendo 64) was even patented, making it perhaps the oldest piece of Nintendo 64 history to date.

Due to the sensitive nature of the build's contents, research on the 1995/07/29 build of Super Mario 64 is highly discouraged, even making its way onto the infamous iceberg discussing Super Mario 64's anomalies.

Speculation
It's likely the 1995/07/29 build wasn't even related to Mario at all, neither created by Nintendo. Instead it was created by an unknown Japanese organisation which created the technology responsible for Super Mario 64's ability to personalise itself to its player's likeness. This build would then be sold to Nintendo and reworked into Super Mario 64.

This build supposedly has an intense texture glitch which causes the textures to change colours rapidly and enduce seziures within playtesters. It's rumoured these playtesters would go on to have horrific and nightmarish hallucinations, which seem to be the origins of some of Super Mario 64's most horrific anomalies.