Star Road

Star Road is an anomalous area found in few personalized copies of Super Mario 64. It is described as a small area found after completing the game (or another special requirement), that leads to several smaller levels referred to as "Challenge Courses".

Geography
Star Road reportedly appears as a floating island shaped like a star, with one or several Toads scattered throughout the area, which supposedly have unique stars in place of the red spots on their heads. There are usually 5 pipes on each end of the area, that would lead to the Challenge Courses connected to Star Road. Notably, due to the rarity of Star Road, only 5 Challenge Courses have been documented: Slippery Slide Mayhem, Moonlight Sanctuary, Deep Dark Abyss, Tubular Tower, and The Champion's Road. Notably, objects representing the Challenge Courses have been documented to be seen in the distance.

Slippery Slide Mayhem
Slippery Slide Mayhem takes the appearance of a long slide with great difficulty. There is usually several obstacles seen in no other slides, such as fire and Chuckyas, as well as several dead ends similarly to those seen in Tall, Tall Mountain's slide. Slippery Slide Mayhem is supposedly the longest slide ever reported, likely due to it's nature as a challenge course.

Moonlight Sanctuary
Moonlight Sanctuary, similarly to the Switch Dungeon level in Floor 2B, is reportedly a challenge course utilizing all caps, as well as Koopa shells (or any anomalous cap or power-up present in the copy). The level itself takes the appearance of an ancient building with several holes in the ceiling allowing moonlight to enter the level.

Deep Dark Abyss
Deep Dark Abyss is a large, dark area that appears to be underground. There are commonly several enemies throughout the level that pose a threat to the player, though they have the unique property of emitting light to make navigating the level easier. This property is not to be confused with Enemy Discoloring, as the enemies appear exactly the same as their regular forms.

Tubular Tower
Tubular Tower is a tall, tower-like level that usually has several obstacles similarly to those from Tick Tock Clock. Climbing the level is reportedly very difficult do to several obstacles and enemies. Many of the few who have accessed Star Road claim to have been unable to pass this level.

The Champion's Road
The Champion's Road is the final Challenge Course, only accessible by completing all 4 other Challenge Courses. No information is available on this course, as very few have managed to complete all 4 other Challenge Courses, or those who have do not speak about The Champion's Road, in a similar nature to those who have found the Eternal Fort.

???
Seen in the only video containing footage of Star Road recorded by BlackJoystick, there is a hidden sixth area found by accessing a distant floating island. This area has not been reported in any other documented instances of Star Road, and what the area itself is is unclear, similarly to The Champion's Road. However, in BlackJoystick's next video, they appear in a strange greyscale castle. Some have theorized this new castle is actually the mysterious area seen in Star Road.

BlackJoystick's Documentation
Youtuber BlackJoystick is one of the few who have reported accessing Star Road, and the only one to get footage of the area. The first minute or so of the video is blank footage, though audio suggests BlackJoystick is in the Eternal Fort. Around a minute into the video, the footage starts and the player falls into a greyscale area resembling Princess Peach's Castle. They walk through a hallway and find a room with a star, and a sign saying to take it. When they collect it, text appears saying "YOU ARE WORTHY". BlackJoystick then appears on top of what appears to be Princess Peach's Castle, though it could be the Eternal Fort. They walk onto a path of rainbows to a see-through platform with a star on it, and get teleported to Star Road.

They talk to a Toad who claims that they are the first to survive the Eternal Fort, and that the team creating Super Mario 64 worked hard on the Challenge Courses found in Star Road. BlackJoystick explores, reading the signs labeling the pipes, and attempts to enter The Champion's Road. However, text appears saying "COMPLETE THE OTHER FOUR" and they are sent back to Star Road. They then stand on an edge of Star Road, and are teleported to a floating island seen in the distance earlier in the video.

BlackJoystick briefly explores the floating island, before finding an entrance to what appears to be a secret area. They read a sign, which says not to enter it and go back to the challenges. However, BlackJoystick doesn't listen and enters the secret area, and the video ends.