The 121st Star

The 121st Star is an anomalous Power Star that can be found in many personalized copies. It was one of the most popular rumors when Super Mario 64 was released, as people believed there might be more beyond the 120 standard stars in the game. The way to get the 121st Star is very inconsistent, likely as a result of playground rumors being blended with true personalized experiences, though some methods are more common than others, likely the actual ones that were found by players.

List of Methods
''Below is a list of some of the many ways to supposedly unlock the 121st Star. Note that some of these may be fabricated due to the widespread nature of this rumor or could be found simultaneously to add up to 122 or more.''


 * Collecting 100 coins outside of the 15 main courses of the game, see 16th 100 Coin Star.
 * Somehow activating the Toad's Tool 64 Star. This is likely impossible, as the star was a glitch in the Toad's Tool device.
 * Grabbing any star from unused courses/sub areas implemented by the A.I.
 * Backwards Long Jumping into an area containing the star.
 * Finding a second Secret Aquarium and obtaining a star there.
 * Completing a seventh mission in any course, despite there only being 6 missions and a 100-coin star in standard copies.
 * Obtaining it from Yoshi upon speaking to him, along with the other gifts obtained from them. This does not happen in standard copies.
 * Reaching the Behind the Waterfall area or any other Minor Anomalous Location.
 * Finding a 4th star-giving Toad.
 * Finding a 3rd MIPS the Rabbit, or Mipsy.
 * Using the Vanish Cap to get behind the mirror in the Second Floor. Notably, this method is a hidden star in Super Mario 64 DS.
 * Obtaining the star at the end of Bowser in the Sky. Notably, this does not increment the star counter in standard copies.
 * Obtaining the Eternal Star, Book on Bad, Discolored Star or another anomalous collectible.

16th 100 Coin Star
Mario can obtain a Power Star for collecting 100 Coins in any of the 15 main courses. As a logical result, many players have speculated on the possibility of obtaining additional 100 coin stars from the game's other levels, or from Princess Peach's Castle. The problem with this is that all the game's secret courses and cap switch stages have less than 100 coins:
 * The Princess's Secret Slide - 80 Coins
 * Tower of the Wing Cap - 63 Coins
 * The Secret Aquarium - 56 Coins
 * Wing Mario Over the Rainbow - 56 Coins
 * Cavern of the Metal Cap - 47 Coins
 * Vanish Cap Under the Moat - 27 Coins

The Castle itself has 15 coins - 2 from the Castle Grounds, 4 more in the First Floor, and the remaining 9 from Boos in the Castle Courtyard.

However, in the Bowser levels - Bowser in the Dark World, Bowser in the Fire Sea, and Bowser in the Sky, it is possible to spawn an unlimited number of coins during the Bowser boss fight. As a result, Mario can get well over 100 coins. Unfortunately, this will not spawn an additional star.

Despite this, some players claim to have obtained an additional 16th 100 Coin Star in some way. Such as by exploring additional, normally inaccessible areas of the Castle, such as the Fourth Floor or Goomba Courtyard, where enemies spawn, allowing Mario to kill them for additional coins.

Trivia

 * A similar rumor exists for the DS version about a "151st" star.