The Final Stretch

The Final Stretch is an anomalous level found in some personalized copies of the Super Mario 64, often found in place of Bowser in the Sky or somewhere on the Fourth Floor of Princess Peach's Castle. This level consistently appears as a final level and last challenge for the player upon completing the rest of the game, leading some to believe it is an early version of Bowser in the Sky or the Bowser level of the Fourth Floor. The level commonly shares it's music with the other Bowser levels, though has reportedly had a remix of the original Super Mario Bros. ' castle level theme featuring a prominent organ.

Description
The Final Stretch is described as a large, temple-like area with very difficult platforming and lots of enemies, such as Fly Guys, Bullies, Lakitus, Bob-ombs, and Fwooshes, though several other enemies have been reported to impede the player's progress such as Amps, Chuckyas and Thwomps. There are several different types of geometry and hazards that have been reported in the level, some being entirely unique, though most appear in other Bowser levels. This re-usage of assets and simplistic design has led some to theorize this level is created through Dynamic Level Arrangement, though this has yet to be confirmed. The level reportedly has the skybox seen in Rainbow Ride, though other reports have claimed different skyboxes can occur, such as the Bowser in the Dark World skybox or just a black void.

The level reportedly has a boss fight at the end, most commonly being against Bowser, though the Cyan Bowser Enemy Discoloring has also commonly been reported in this level, with dialogue specifically referring to the anomaly as Bowser's Brother, the character this instance of Enemy Discoloring appears to imitate. Notably, Bowser's Brother has also been reported to appear as a halfway point, as well as other bosses such as Big Bullies and King Whomp. This may mean the level was simply a bonus level due to using a different character as a boss, that there would have been multiple types of bosses in Bowser levels, similarly to Super Mario 64 DS' levels containing characters that are unlocked by defeating bosses, or simply that this discoloring's increased difficulty fits with the rest of the level.

Upon clearing the level, the reward is most commonly just a Power Star, making this a viable method to obtain a 121st Power Star, though other rewards have been reported, such as a new ending or key to another floor, such as the Fourth Floor, all appearing to somewhat mimic the rewards for clearing Bowser levels in the base game of Super Mario 64. This is another piece of evidence used by some to suggest that it is was a scrapped Bowser level, or an early version of Bowser in the Sky.