In the Japanese version, the fourth HUD option is designed after a Japanese calligraphy sheet. In the international release, this is replaced with a new design based on crayon scribbles.

Within the game's data are early portraits depicting each of the game's protagonists and the Animal Friends, the latter of whom don't appear in the final release outside of cameos as Stone + Cutter Kirby's forms. Pre-release screenshots show these and similar portraits appearing in the game's HUD, not only corroborating earlier indications that Waddle Dee, King Dedede, Adeleine, and Ribbon were playable at an earlier point in development, but also indicating that the Animal Friends were planned to play a proper role at one point.

In 2021, a speedrunner working with a group effort to decompile the game uncovered a cheat code that can turn a 0% save file into a 100% save file, likely used by the game's developers for debug purposes. To use the code, you must first plug in two controllers, turn on the game and create a new save on File 3. It does not matter if there is save data or not on File 1, but File 2 must have no save data. Then reset the game and, using the second controller, hold L when the Nintendo & HAL Laboratory logos appear and press C-Up/C-Up/R/C-Right/C-Left/Start. The 1-Up sound effect will play if done successfully, and File 3 will now hold a 100% save file.

This code can be executed on every release of the game except for the Wii Virtual Console release due to the lack of C-Button mapping for that version.

The boss of Shiver Star, HR-H, has a second phase known as HR-E that chases Kirby down the metallic road they are fighting on while the road's tiles fall away behind it. If you take too long to defeat HR-E by using up the nearly 4 minutes this segment lasts for, new road tiles will stop generating, creating a dead end that forces Kirby into a bottomless pit, losing the fight.

Found within the game's data is an unused Victory Dance Remix of when Kirby clears a level that's been used in various Kirby games over the years.

In level 3 of Neo Star, the word "KIRBY" can be found spelled out in rock formations towards the end of the level.

There was an early idea for a music based mini game in which players would play along to sheet music with Kirby, Ribbon, Adeleine, and King Dedede, but it was never implemented.

In the Japanese release, the sandwich was originally an onigiri. This was due to Nintendo regulations on Japanese culture when games were translated overseas. Oddly, Waddle Dee eats a onigiri during the stage ending picnic sequences in all versions.

The electric/cutter mix ability is most likely a reference to Darth Maul's dual sided lightsaber from the film Star Wars Episode I: The Phantom Menace.

Masahiro Sakurai (the creator of Kirby) provided the voice of King Dedede.

Shiver Star, the game's 5th world, appears to be a frozen-over version of Earth, containing several uninhabited urban areas. Nintendo has confirmed that Shiver Star was once inhabited, but the climate drove them to evacuate the planet. This has led fans to speculate that Shiver Star is a post-apocalyptic version of Earth. Though Nintendo's intentions during the making of Shiver Star remains unknown, it can be inferred that the world is either a message about climate change, or the suggestion that the "Kirby" series takes place in our own universe.

Prerelease screenshots hint that King Dedede, Adeleine, and Waddle Dee were playable at one point during development.