Key

Keys are collectibles in Super Mario 64 found by defeating Bowser. They take the appearance of yellow keys with horns around them. There are 2 keys in standard copies of Super Mario 64, obtained from Bowser in the Dark World and Bowser in the Fire Sea. These keys unlock the Basement, and the Second Floor.

Extra Keys
The Third Floor does not require a key in standard copies. 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.

Key Removal
In some personalized copies, 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 include 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, most commonly Floor 2B.