Power Moons

Power Moons are anomalous collectibles found in some personalized copies of Super Mario 64. Power Moons have been described as having a design very similar to their appearance in Super Mario Odyssey, though simplified in order to fit the Nintendo 64, or appear as a full moon instead. Power Moons are notable collectibles as they reportedly have their own anomalous part of Princess Peach's Castle, nicknamed the Moon Courtyard.

Description
Power Moons generally appear as replacements for the Power Stars of Super Mario 64, simply being a different appearance for the Power Star. However, there are several reports that Power Moons are their own collectible alongside Power Stars. Power Moons have oddly been reported to function in a similar manner to red coins, though are more commonly reported as full-fledged collectibles. Power Moons that appear this way are rarer than Power Stars, and are usually just for completion, though can unlock certain levels or areas, particularly the Moon Courtyard if it isn't unlocked or located some other way.

The Moon Courtyard
The Moon Courtyard is an anomalous replacement of the Castle Courtyard that can reportedly temporarily manifest when significant progress is made in the game, in a similar manner to the Castle Garden. It usually is unlocked by collecting enough Power Moons, though can be found through some other way like finding a secret entrance somewhere in the castle, such as a window in the Internal Garden.

The area itself is usually described as a grassy area with several bushes and trees barricaded with white brick walls that form a pentagon. One of the walls is connected to Princess Peach's Castle, allowing the player to return to the castle. No enemies, NPCs or even levels have been reported in this area. The Moon Courtyard reportedly contains several Power Moons hidden around the area to be collected.

Upon all Power Moons being collected, several reports state an event of some kind occurs, the most common being the door to the castle opening, having been locked beforehand, though other reports have referenced other changes like moon or night-related levels appearing, or a new area appearing. An oddly consistent feature is that after leaving the Moon Courtyard, a strange moon statue can appear in place of the Eternal Star Statue in the castle courtyard or the Internal Garden. The relevance of this statue is unknown.