This information comes from an Iwata Asks interview with Kensuke Tanabe…
– Miyamoto wanted to make a new Donkey Kong game, was looking for a developer
– Kensuke Tanabe remembered the Retro CEO had worked on Donkey Kong previously
– Retro CEO suggested the codename F followed by the numbel 8 (so it read as fate)
– Decided early on to base it off the original Donkey Kong Country
– Diddy Kong has a jetpack
– If you hold the button after jumping, he can hover
– If you do it while Diddy Kong is on Donkey Kong’s back, Diddy Kong can carry Donkey Kong along with him
– Moving around is easier
Thanks to Robert for the tip!
