Metal Cap

The Metal Cap is the third and final cap in Super Mario 64. It is found in green ! boxes, and is Wario's Power Flower ability in Super Mario 64 DS. It is unlocked in Cavern of the Metal Cap. It weighs the player down in water, destroys most enemies on contact, and renders the player relatively invincible. In future games, it appears as a seperate entity than Mario, oddly.

The Metal Parasite
The Metal Parasite is an enemy that can appear in certain personalized copies of Super Mario 64. When touched, the player will gain an alternative form of the Metal Cap.

Metal Wings
Despite being unable to collect both the Metal Cap and Wing Cap at the same time, there is an unused texture for metallic wings. Using hacks, it is possible to have both caps on and see the wings.