A mock-up of its appearance.
The Level Locked Screen is an anomaly typically appearing in Beta Builds of Super Mario 64, and appears when a course is either incomplete or unable to load. It is generally believed to be either set by the A.I. or manually by developers.
Description[]
It has been most frequently described as a white screen with the sprite of Mario from Super Mario Bros. and flashing text stating, "LEVEL LOCKED, PLEASE RESET THE GAME," although the text may vary depending on its location. Its activation is also inconsistent, with one attempt to enter a level resulting in the screen and another simply just crashing the game as a result of attempting to load garbage data. Occasionally, the screen itself will also result in crashing for unknown reasons.
Crashes directly resulting from the screen have also occasionally resulted in data loss. These properties of the screen indicate that it does more than what could be initially assumed, although what is exactly is currently unknown.
Presence in Finished Copies[]
Although most finished cartridges should have no need for the screen to appear, it can anomalously lock one out of a level anyways. If repeated, it can render a cartridge impossible to complete without further modifications. Similarly, in the event the screen does not appear, the course it had previously locked someone out of will equally have a chance of having been converted into garbage data, generally resulting in a crash.
Peculiarly, this will happen most often with Rainbow Ride for unknown reasons, although theorized to be as a result of something in the course affecting the A.I. Another common course this is reported with is Cool, Cool Mountain, similarly for unknown reasons.