Rabbit

Rabbits are a species within the Super Mario series. In Super Mario 64, MIPS the Rabbit appears as a character in the castle basement. However, in the game's remake, Super Mario 64 DS, MIPS is replaced by an assortment of unnamed rabbits that spawn upon talking to the Toad in the Rec Room. These unnamed rabbits can also be found scattered around the castle with positions and colors dependent on the character that's currently being played. These rabbits will drop keys for the corresponding character's minigames. Yoshi's rabbits are yellow, likely a reference to MIPS, Mario's rabbits are pink, perhaps a reference to Mipsy or just the unused MIPS model, Luigi's rabbits are green, and Wario's rabbits are orange. The character-specific rabbits can only be found when playing as their respective characters. There is also a type of rabbit that appear white and glowing and will drop keys to unlock one of the castle's secret stars after eight stars have been collected. Eight of them can be found in the game, and spawn in place of any other rabbit that has already been caught. A yellow rabbit appears in the hedge maze in the corner of the Castle Grounds that drops the key to the castle, and is the only rabbit required to beat the game without 100% completion.

Purple Rabbit
In the game manual of Super Mario 64 DS, an odd image of a purple rabbit can be seen. Such purple rabbit has never been seen in the game, leading some to believe it is unused. This has been attributed to Waluigi, likely due to the purple coloration, or perhaps an early color for another one of the playable characters. However, some believe it is just an error and it is actually meant to be Mario's pink rabbits.

In some personalized copies, the Purple Rabbit can actually be found, usually for minigames played as Waluigi if they are unlocked. However, some have claimed they have to be found to unlock Waluigi, dropping Waluigi's key upon being found. Other reports say they drop the Big Star Key item, which in itself varies in use. It most commonly spawns after finding every other rabbit, including the glowing rabbits.

In-Course Rabbits
Every rabbit appears in Princess Peach's Castle in Super Mario 64 DS. However, some have claimed they can be found in levels. For example, a rabbit on the top of Bob-omb Battlefield's mountain in any mission where Big Bob-omb or Koopa the Quick aren't present. They are always just repositions, though, instead of holding new minigames. This is likely the Personalization A.I. trying to make the game harder for the player.

Mechanic Reversion
According to some reports, instead of the rabbits unlocking the minigames, all of them except the glowing rabbits and Castle Grounds rabbit disappear entirely, with the minigames naturally being unlocked. The glowing rabbits also most commonly appear in the basement. This is frequently believed to be the A.I. attempting to recreate MIPS' appearances in the original game, just using the glowing rabbits as a placeholder.

Trivia

 * In Super Mario 64 DS, the rabbits are internally known as "MIP" and drop "MIP Keys". This is an obvious reference to MIPS the Rabbit, their predecessor.