Ice Key

The Ice Key is a key composed from ice. It is one of the seven Stop 'n' Swop items from Banjo-Kazooie, along with the six Mystery Eggs. In Banjo-Tooie, the Ice Key is used for obtaining the Mega-Glowbo, which enables Kazooie to transform into a dragon.

Banjo-Kazooie
In Banjo-Kazooie, the Ice Key appears in a large alcove in Wozza's Cave, although it is blocked off by an indestructible wall of ice.

To dissolve the wall, Banjo and Kazooie must enter the Sandcastle of Treasure Trove Cove and enter a sentence reading "CHEAT NOW YOU CAN SEE A NICE ICE KEY WHICH YOU CAN HAVE FOR FREE" (without spaces). When the duo obtain the Ice Key, it appears in the Stop 'n' Swop menu. However, the Ice Key does not have any other purpose in the game.

Banjo-Tooie
In Banjo-Tooie, Banjo and Kazooie can obtain the Ice Key by destroying a Banjo-Kazooie Game Pak enemy in Jinjo Village. Upon obtaining the item, the duo must enter the Waterfall Cavern of Glitter Gulch Mine, destroy a Talon Torpedo Door, and swim through the tunnel leading to the icy portion of Hailfire Peaks. The Ice Key is used to unlock a large safe with the powerful Mega-Glowbo allowing for Humba Wumba to transform Kazooie into a dragon.

Banjo-Kazooie: Nuts & Bolts
In Banjo-Kazooie: Nuts and Bolts, there is an imprint of the Ice Key on Boggy's Gym. If the Ice Key was obtained in Banjo-Kazooie, a Mumbo Crate appears on the roof of the gym. By taking it to Mumbo's Motors, the player unlocks the British flag for a vehicle customization option.

The Ice Key itself makes a cameo in the melted Snowman of Banjoland. The Ice Key can be obtained in the Terrarium of Terror and given to a Jinjo, who says he will "swop" the Ice Key in exchange for a Jinjo Token. After receiving the Ice Key, the Jinjo ponders over the mystery of it.

Xbox Live Arcade ports
Stop 'n' Swop was repurposed for the Xbox Live Arcade remakes of both Banjo-Kazooie and Banjo-Tooie. The Ice Key cannot be obtained in the Banjo-Kazooie port unless the Xbox 360 has a save file for the Banjo-Tooie port or Banjo-Kazooie: Nuts & Bolts. If the player obtains the Ice Key but does not have a save file for either game, the game and its achievements cannot be saved.

In the Banjo-Tooie port, the Banjo-Kazooie Game Pak of Jinjo Village contains the Gold Mystery Egg instead. If the Ice Key was collected in Banjo-Kazooie, it automatically carries over into Banjo-Tooie.

Trivia

 * There is ASCII text for "ICE KEY" hidden in Donkey Kong 64. By using a GameShark code, the player can even add it to the "Totals" menu (although it has no icon). The Ice Key cannot be removed after being adding, even if the player starts a new save file. Like with Banjo-Kazooie, the Ice Key does has no function, and its intended purpose is unknown.