It is well known that many Nintendo projects are cancelled during development, and one title that was announced in 2004 for the GameCube that did not see the light of day was a Kirby platformer. The game was known simply as Kirby for Nintendo GameCube, and was announced a year after Kirby Air Ride. An interview with the late Satoru Iwata revealed that HAL Laboratory had been working on a new Kirby game since 2000, after Kirby 64: The Crystal Shards came out, with a game eventually seeing light on the Wii as Kirby Return to Dreamland.
YouTuber Foulowe56 discovered some footage from the game back in January, with a 9-second clip, and Twitter account @ObscureKirby has since shared a new round of footage showing off some typical Kirby power-ups along with some fancy camera angles and unusual-looking levels.
The cancelled project appears to be a mix of 2.5D and 3D environments, much to Kirby 64. There appears to be a variety of concepts that would be seen in other games such as enemies stacking up and helping Kirby out, which later appeared in Kirby Star Allies.