Key

Keys are collectibles in Super Mario 64 and Super Mario 64 DS. There are 3 key types: The Bowser keys, the character keys, and the star keys. The Bowser keys are dropped by Bowser in Bowser in the Dark World and Bowser in the Fire Sea. They take the appearance of standard yellow keys with horns, and unlock the Basement and Second Floor of Princess Peach's Castle.

The character keys and star keys are only found in Super Mario 64 DS, excluding supposed manifestations in personalized copies of Super Mario 64. The character keys are dropped by Goomboss, King Boo and Chief Chilly in Goomboss Battle, Big Boo Battle and Chief Chilly Challenge respectively, and they unlock Mario, Luigi and Wario, also respectively.

The star keys are used to unlock minigames in the Rec Room, and are found by catching Rabbits around Princess Peach's Castle after talking to a Toad in the Rec Room that will cause the Rabbits to spawn. A star key obtained by collecting all 8 glowing Rabbits can also unlock a door containing a castle's secret star. There is also a star key that unlocks the castle and is required to continue the game.

Extra Keys
The Third Floor does not require a key in standard copies of Super Mario 64. However, some reports claim that a Bowser level on the Second Floor contains the key required to unlock the Third Floor. Extra keys can also appear to unlock the First Floor, usually being found from finding MIPS in the Castle Grounds similarly to Super Mario 64 DS. Keys have also been reported to appear to unlock anomalous floors, such as the Fourth Floor. Another reported usage of keys can be to unlock the cannons in levels instead of talking to Bob-omb Buddies.

Key Removal
In some personalized copies of Super Mario 64, doors requiring keys are replaced with doors requiring a certain amount of stars. Notably, Bowser levels usually do not get removed, with the key dropped by Bowser being replaced with a star, similarly to early builds of Super Mario 64. However, Bowser levels have been reported to be removed, and instead replaced with another special level.

Other Key Types
There are 2 anomalous key types that do not take the appearance of regular keys. These are a key with the Metal Cap texture known as the Metal Key, and a key held by a Boo known as Big Boo's Key. The Metal Key can unlock special floors or a secret part of the castle, while Big Boo's Key usually unlocks rooms in Big Boo's Haunt, though it can also unlock special floors of Princess Peach's Castle, most commonly Floor 2B.

DS Key Manifestations
In some personalized copies of Super Mario 64, the character keys and star keys from Super Mario 64 DS can reportedly appear in the original game with similar, identical or entirely different uses. The character keys usually function exactly the same or unlock a level tied to the corresponding character, but the star keys have several reported uses, such as replacing Bowser keys, minigames in the Rec Room if they are present, special rooms in Princess Peach's Castle, or nothing potentially due to Personalization A.I. limitations.

Extra Key Types (DS)
Several keys can reportedly appear in personalized copies of Super Mario 64 DS, likely due to their increase in relevance in the remake. The most commonly reported one is a character key that unlocks Waluigi, usually being a character key with an upside-down L in the middle of a round hole on the end, sometimes with a Waluigi hat on top of the key. There is also an unused model that is a bigger star key, fittingly named the Big Star Key. Functionally, it just unlocks the castle like the first key the player obtains, but some have claimed it unlocks special areas upon being obtained, or functions as another design for the Waluigi key. These keys themselves are inconsistent on how you unlock them, but the Waluigi key can commonly be found in levels such as the Piranha Pit or Rabbit Meadow, and reports claim both keys can be obtained from the Purple Rabbit. Some reports also talk of a "halved key" for Mario, with one half being in Goomboss Battle and the other being in Bowser in the Dark World, allowing Yoshi to fight Bowser, which is usually impossible. How exactly Bowser is defeated with Yoshi is inconsistent, but the most common explanation is that Bowser can throw Bob-ombs that Yoshi can throw back, similarly to Big Bob-omb.