Banana Fairy Secrets
By taking pictures of banana fairies throughout the game, you can unlock several secrets in the "Mystery" section of the main menu. First off, you need the camera. To get it, take Tiny Kong to the large structure on the DK Isles that looks like a fairy's head. Jump in the barrel to shrink, and go inside to get the camera from the large fairy within. Then you can take pictures by holding Z and pressing Down-C. As you progress through the game, taking pictures of any fairies you find will unlock options in the Mystery menu. Depending upon how many fairies you catch in this fashion, certain things become available:
Two Fairies - DK Theater - Here, you can watch all of the cinema scenes that you've already found in the game.
Six Fairies - DK Bonus - This menu let's you fool around in a few bonus minigames. Once you find Rambi and Enguarde in the main game, you can play as them in their own battle arenas. Plus, once you beat the Donkey Kong and Jetpack arcade games, they become available to play in this menu as well.
Ten Fairies - Bosses - Fight all the bosses that you've encountered in the main game to your heart's content. Not the final battle, though...
Fifteen Fairies - Krusha Battle - This simple menu let's you activate Krusha in the battle modes. He shoots exploding oranges out of his bazooka, giving him an advantage over those other measly apes.
Twenty Fairies - Cheats - A variety of options, such as unlimited ammo and invincibility.