Timer

The Timer is an anomalous feature that can appear within some highly personalized copies of Super Mario 64. As it's name suggests, the Timer counts down from a specific amount of time to zero, and is believed to cause an as-yet unknown effect once zero is hit. It is generally believed that you should complete the game before the timer ends, as these effects are generally believed and rumored to be harmful.

Behaviour
The Timer most commonly counts down from an interval of between 15 to 20 hours. Time is only elapsed while playing the game, and the countdown does not continue when the game is paused or shut off. The countdown usually starts when the player firsts enters the castle and stops when the player beats the game, although these conditions can vary from copy to copy.

The Timer can take a variety of forms depending on the personalized cartridge you are playing. Usually, the Timer is displayed as part of the H.U.D, but it can also take the form as a part of the pause menu, an ingame object such as a clock or NPC, or some combination of the aforementioned. It has even been reported by some that a heavily personalized version of Tick Tock Clock (usually moved to the first floor) can act as such an interface to read and interact with the Timer.

Several actions can cause the timer to add or remove time from the amount currently remaining. Positive actions, such as collecting secret stars, can add time to the timer. However, the main danger from this effect is the time lost due to dying and getting game overs. Loss of lives and game overs can cause time to be quickly lost, making the race against time ever more dire.

It has been noted that a Negative Emotional Aura similar to the one experienced while playing Wet-Dry World tends to occur when the Timer is active. Feelings of dread tend to manifest and intensify the closer the timer gets to zero.

Theories
It is believed that the Timer acts as an obstacle which causes negative consequences such as a bad ending or the deletion of save files. It is unknown what these consequences are, but as with all personalized copies, the effects will likely vary depending on the cartridge. It is believed that the Timer may be added by the A.I to challenge skilled players.

The Timer could also be a cut element from beta versions of the game. The Timer may take inspiration from the clock on the outside of the castle, and the original clock may have served a purpose to tell the time remaining (and still does in some copies). It is also possible that the Timer also once acted as a time limit for demo versions of the game.