From the Super Mario Wiki
Artwork of an Orange.

First appearance

Donkey Kong 64 (1999)
“Squawk! Pick up the Oranges and hold Z Button, then press Camera right Button to throw them.”
Squawks the Parrot, Donkey Kong 64
DK64 Orange Grenade.gif

Oranges are collectible weapons that appear in every world of Donkey Kong 64, and their purpose is to be used as grenades. Appearance-wise, Oranges look identical to normal oranges but with a grenade pin on top. The active Kong can throw Oranges if the player presses Camera right Button while holding Z Button. Oranges can also be thrown in mid-air. They can defeat most enemies and are sometimes used in puzzles. Klumps and Mechanical Zingers attack with green oranges. Klumps are sometimes seen eating them from afar and belching.

Oranges first appear in one of Cranky Kong's Training Barrels. By default, the Kongs can only carry a maximum of 20 Oranges. They can purchase ammo belt upgrades from Funky Kong to slightly increase the limit to 25, and later 30.

Oranges' explosions cause the game to lag, which is compensated from speeding up the Kong. The lag can be abused to bypass the collision detection of certain walls, such as the one blocking the entrance to the Angry Aztec lobby. This is ineffective in the Wii U's Virtual Console release, which has a more consistent framerate.

Oranges are also used in Multiplayer mode, where they create an identical shockwave attack to that of a Kasplat's. Krusha also uses Oranges as ammo for his orange grenade launcher.