Internal Clock

The Internal Clock is a supposedly scrapped mechanic in Super Mario 64 that would track the time of the player's timezone and change the game to adapt to the time of day. It is demonstrated in this video. It also has a calendar to change for different events. It was likely removed due to time constraints, possible glitching, and more ambition than possible using the Nintendo 64.

Night-Time

 * All levels will have night skyboxes.
 * The walls of the castle will change to that of the Third Floor.
 * Wing Mario Over the Rainbow will change to Wing Mario Over the Starry Sky.
 * The star painting on the Second Floor will lead to Starry Skyline.
 * Lethal Lava Land will have blue lava.
 * Toads will become Star Toads.
 * Music will change to use the Piranha Plant's Lullaby instruments.

Day-Time

 * The sun painting on the Second Floor will lead to Sky Seas.
 * Starry Skyline changes to Sunny Skyline, with a daytime version of the Starry Skyline painting.

Halloween

 * Boos will appear in several more levels.
 * New "scary" levels will be able to be found, such as Big Boo's Forest.
 * Music will be changed to use Big Boo's Haunt's instruments.

Christmas

 * All levels will be covered in snow.
 * It will be snowing in all levels.
 * Music will be changed to use the Cool Cool Mountain instruments.