While bug testing the final release developers at Rare encountered a game breaking bug when playing without the expansion pack, however the bug disappeared whenever the expansion pack was plugged in. Programmers could not locate the cause of the bug in time, so instead of delaying the game, Rare simply listed the expansion pack as a requirement to play.
In the game, you get to play the classics Donkey Kong (1981) and Jetpac (1983) during different stages.
In Donkey Kong's treehouse, there's a picture of a dolphin. Dolphin was going to be the name for Gamecube, and was probably still in use at the time the game was made.
The game is one of the few on the Nintendo 64 to require the optional Nintendo 64 Expansion Pack to play: fearing that too many parents would buy this as a Christmas present while forgetting to buy the expansion pack, Nintendo made the unusual move of only selling the game with the pack included. This caused some level of controversy as the expansion pack had been available for at least a year prior to the games' introduction, and the bundle of the game + the expansion pack cost more than a stand alone N64 title.
The spirit of Wrinkly Kong from Donkey Kong Country 3: Dixie Kong's Double Trouble! (1996) appears in every stage's "lobby" giving you hints to complete the levels.