Parental Control

Parental Control is an anomalous feature found in some personalized copies of the game. The purpose of it is probably for controlling the time a player can use the game. Most of the times, it'll replace the STEREO button, possibly making it to be easier to reach.

Phenomena
The Parental Control feature is an anomaly that can be found in a few copies. Most of the times, it'll replace STEREO on the File Select screen, and would feature a setting screen once opened. It's hard to confirm if this screen actually exists, because the contents are very inconsistent. But in the first report, the parental Control screen would have the features below:

A time-setting feature: The user can set how long time would the game be playable every day. Content blocking: This could choose which levels the player can play, and what levels should be blocked and un-enterable. This setting can be used to find out which levels are in a copy.

Password: This is a tricky one to explain. When a user wants to set the password, they need to first move the control stick to this option, then press Start. The user would then be able to set a password, which is a combination of keys or control stick moving. When the user wants to stop recording the password, they can just press Start again. The password is required to change the settings, extend playable time, and to allow or deny a level.

Theorizing
It is theorized that this feature was once made by Nintendo to prevent kids from being addicted but was cancelled due to unknown reasons. From the time-setting option, we can see that this feature uses the Internal Clock, so Parental Controls might have been cancelled to hide the trails of the Personalization A.I.