Banjo-Threeie is a cancelled video game that was developed by a British video game developer Rare and was initially going to be published by Nintendo, and later Microsoft Studios (Microsoft Game Studios at the time). The game was going to be the third installment in the Banjo-Kazooie franchise. It was initially developed for the Nintendo GameCube, and later due to Microsoft's purchase of Rare, Xbox and Xbox 360. It is rumored that parts of Banjo-Threeie are present in Banjo-Kazooie: Grunty's Revenge for the Game Boy Advance.
At the end of Banjo-Tooie, released for the Nintendo 64 in 2000, Gruntilda Winkybunion (the franchise's antagonist) hints of Banjo-Threeie, telling the player she will return in that game.
Spaceworld 2000 Tech Demo
At Spaceworld 2000, a video game event, a few tech demos for the Nintendo GameCube were shown. Demos for games such as Luigi's Mansion, The Legend of Zelda: Twilight Princess and Super Smash Bros. Melee were shown there. A tech demo titled Banjo-Threeie was also shown. It is speculated that after Gruntilda was defeated in Banjo-Tooie, her henchmen would try to get revenge against Banjo and Kazooie. In the tech demo, Banjo and Kazooie are pursued by a horde of enemies, which could mean that the tech demo shown could have shown the initial plot of Banjo-Threeie. Gregg Mayles (creative designer at Rare) has stated on Twitter that a Banjo game for the Nintendo GameCube was never planned.
After Microsoft's purchase of Rare, in 2002, a build titled Banjo-X was found on an abandoned Xbox development kit, which was dated June 2004. Unfortunately, while attempting to boot the code, a black screen would show with white text that says that some files are missing. Only one level, Mumbo's Mountain, was made for Banjo-X and a few items were discovered in the build. The items were Springy Shoes, Rocket Sneakers, Metal Feathers, Aviator Goggles, Invisibility Chocolates, Big Feathers, Bag of Eggs and Diamond Beak. Character models of Conga, Mr. Termite, and Mumbo were shared on Twitter by two of the game's developers.
It is unlikely, though, that this was part of the development of Banjo-Threeie. When a fan asked if Banjo-X was either a remake of Banjo-Kazooie with a co-op mode or if it was a new game, Steve Mayles, one of the game's developers, responded by saying "I remember 4 Banjos running around, but not much work was done on design, I don't think. Or levels." He also confirmed that the art style that was used in Banjo-Kazooie: Nuts and Bolts was settled on in early development.
In a different tweet, Ed Bryan (another developer of the game) confirmed that in the Mumbo animation, Mumbo said "Come and have a go if you think you're hard enough", and that it was a new model made to see if lip-syncing was possible with the mumbling speech used in the Banjo-Kazooie franchise. He also confirmed that the animation was made circa 2004. It is rumored that the game would've broken the fourth wall and the all characters would gradually become aware that the game was a remake/remaster of the original Nintendo 64 version, which could have lead to interesting events.
Steve Malpass (another developer of Banjo-X) stated "All the puzzles and tasks in that level--we would see how we could adapt them. Conga the Ape, for instance, would realize he had fought Banjo and Kazooie on Nintendo 64 and act differently." Items from Banjo-Tooie in the game would also be a possibility. If this was the case, there is a possibility that Banjo X was Banjo-Threeie, but it is more likely that it was a remake/combination of the previous two games.
Focusing on Nuts & Bolts
Later in development, the developers began to believe that the game wouldn't sell because fans would have wanted a new Banjo-Kazooie game, and not a remake, so the development team decided to mix Banjo-X and Banjo-Kazoomie into a new game.
In this game, the player would have had constant access to vehicles and vehicle construction. The team still wanted the game to stay similar to the previous two games, but Microsoft decided to focus on vehicle access because it was a unique concept that could be added to a puzzle game. Because of this development, the game became Banjo-Kazooie: Nuts & Bolts.
In 2006, a trailer for a possible new Banjo-Kazooie game was released. In it, Banjo and Kazooie find a door, open it and find a world full of Jiggys, Music Notes and Honey Comb Pieces (the franchise's collectible items). They ran around the world, crash into a wall, and the trailer ends.