Frog Cap

The Frog Cap is an anomalous cap in Super Mario 64, appearing to be the Frog Suit from Super Mario Bros. 3. As you would expect, it allows the player to have infinite health underwater. The Frog Cap usually manifests in water levels where it is most useful. The Frog Cap is a relatively rare anomaly, likely due to there only being 3 water levels in the base game and the A.I. would likely struggle to implement a new cap, unused or not.

Description
The Frog Cap has been described to function very similarly to how it worked in Super Mario Bros. 3, though now in Super Mario 64. It gives the player infinity breath underwater, and occasionally faster swimming speed. Some players have also reportedly obtained a higher jump from the Frog Cap, likely due to the Frog Cap's nature of being based on Frogs, who are known for having a higher jump.

The Frog Cap is supposedly found most commonly in water levels, though has reportedly been found in other random levels due to it's occasional ability to increase the player's jump which could be useful to navigate some areas. It most commonly appears in a light green or cyan box, depending on the color of the Cap Switch.

Unlocking
The Frog Cap is reportedly found in a level typically known as "Frog Cap in the Flooded Tunnel" which most commonly takes place under the lake in the Castle Grounds after the player somehow manages to drain the entire lake in a similar fashion to reaching Vanish Cap Under the Moat, usually revealing a hole or Warp Pipe to the level. The level itself is described as a large cavern filled with water, probably from the drained lake, which requires the Frog Cap to swim through. The end of the level has the level's Cap Switch, usually light green or cyan, just like the boxes that contain the Frog Cap. Like all other Cap Switch levels, the Frog Cap typically contains a Power Star for obtaining 8 red coins. Notably, the level has also been reported to have a hidden Power Star somewhere in the level that requires the player to use the Frog Cap to swim deeper into the cavern to reach the star.