Groovy Grove

Groovy Grove is a supposed course present in certain personalized copies of Super Mario 64. It can be commonly accessed by climbing up a discolored and/or out of place tree somewhere in Princess Peach's Castle, usually in areas such as the Castle Grounds or the Courtyard.

The course is notable due to its music track is unique every time it is entered, implying music generation of some kind. Some have reported limited adaptive audio (i.e. a drum loop being added to the music track when an enemy is pursuing Mario), though these claims are unsubstantiated and rare. The music generation is reportedly not sophisticated, with some either describing the music as discordant or not following musical conventions, others have described the music as merely taking portions of already-existing ingame music tracks. Few have described the music as "good" in any capacity, those who have often wish they could have recorded it in some way.

Description
Groovy Grove is usually described to be in the same vein as a secret course such as The Secret Aquarium, as well as taking longer to load as opposed to a normal course. The course itself is commonly described as a somewhat vast grove, filled with trees for Mario to climb on and larger trees made out of geometry unable to be climbed. If one were to angle the camera upwards, the larger trees usually appear to be incredibly tall. If climbed, the smaller trees may occasionally provide coins, 1-ups, enemies (rarely), Hoot (rarely) or even a star (depending on the mission of the course). The course rarely contains enemies, but has been reported to on occasion, specifically in reports regarding adaptive audio in the level. If the level does feature enemies, they are often Goombas, enemies besides them, if even present, are inconsistent.

Note blocks (also written as noteblocks), present in some previous two-dimensional platformers in the Mario series but notably absent from Super Mario 64, have also been reported to appear in the level, usually either acting as multi-use, stationary Spindrifts or a version of the trampoline. Many have reported that the music itself affects aspects of the level, such as how high the note blocks bounce you into the air or how moving platforms move (if they are present).

The time of day of the course is reportedly inconsistent between personalized copies.

Mission
The mission featured within Groovy Grove is inconsistent, with some more common than others. The most common mission consists of individual platforming challenges to collect 8 red coins, these platforming challenges may use a combination of trees and note blocks, one or the other, or neither. While the difficulty of these platforming challenges is inconsistent, they are commonly described as being "somewhat difficult" as opposed to other platforming present ingame. A second, less-reported mission is to check every tree in the level for a star, most reports mention the player becoming frustrated if this is the mission present. A third, little-reported mission is to find a specific tree, similar (if not identical) to the one used to access the level containing Hoot, the player can then use Hoot drop down on a branch of a larger tree with a star on it. Some have also reported a 100-coin star, though this is rare.

Theorizing
It can be inferred that Groovy Grove, from its music, was used to test how the Personalisation A.I. would handle generating music. The course was most likely scrapped due to the music present in the level commonly not sounding pleasing, though this is just speculation due to the A.I. having the means to make "good" music, as stated by some reports. The longer load times associated with the course also corroborate this theory.

The lack of much of anything within Groovy Grove, despite its somewhat vast nature, implies it was meant to be a full course that went unfinished. The course was therefore likely reimplemented by the Personalisation A.I. as a secret course.

Some have theorized the climbable trees present in the course to be saplings of the larger trees, though this is merely contextual.