Kirby GCN

Kirby GCN (also referred to as Kirby: Legend of the Stars and Kirby Adventure) is the common unofficial title referring to any of the three 3D games that were silently cancelled; of the three, only the first incarnation was widely documented. Nintendo had not released any further info about this game's status for a long period of time, as well as having removed the game's page from their website. There had been conflicting reports on whether the game had ceased development or if it had shifted to the Wii or 3DS - it was speculated to have even been replaced by another game such as Kirby Super Star Ultra.

Some aspects of each of the three individual developments carry over into Kirby's Return to Dream Land, and it wasn't until the release of Kirby's Dream Collection: Special Edition that it was revealed KRtDL was the successor to Kirby GCN.

Story
All that was revealed about the original storyline is that King Dedede stole Kirby's Warp Star and Kirby is trying to get it back. This bears no similarity to the story in Kirby's Return to Dream Land.

Gameplay
The original version of the game in development featured a variation of the Helper System from Kirby Super Star where up to three helpers can be created at once. They can then be controlled by up to three players or by the computer. It is possible that the game had a 3D playing field. A stacking system had also been revealed where Kirby and his helpers can ride on each other's back (possibly creating new attacks). Looking at images, it is assumable that the helpers you make would've be either yellow, green or blue. Looking at past games, yellow is assumably for 2nd player, blue is for 3rd player and green is for 4th.

Abilities
A total of 16 abilities were known to have appeared in this game, but it's likely more were planned to appear during development. Some abilities would've had a different design to them, a feature that had been passed on to Kirby's Return to Dream Land.
 * Beam
 * Bomb
 * Clean
 * Cutter
 * Fighter
 * Fire
 * Hammer
 * Ice
 * Parasol
 * Plasma
 * Stone
 * Sword
 * Tornado
 * Water and/or Bubble
 * Wheel
 * Wing

Helpers

 * Waddle Doo
 * Blade Knight
 * Bonkers
 * Unnamed Water/Bubble enemy
 * Golem
 * Broom Hatter
 * Unnamed Tornado enemy
 * Unnamed Bomb enemy
 * Chilly
 * Flappy
 * Parasol Waddle Dee
 * Sir Kibble
 * Wheelie
 * Heat Phanphan
 * Plasma Wisp
 * Knuckle Joe

Piggyback Helpers

 * Bonkers
 * Flappy
 * Heat Phanphan
 * Wheelie
 * Golem

Non-Copy ability Enemies

 * Waddle Dee
 * Scarfy
 * Blipper
 * Bronto Burt
 * Dale
 * Babut

Bosses

 * Whispy Woods
 * HR-D3

Trivia

 * The large robot resembling King Dedede (later named HR-D3) that Kirby was seen fighting against in the trailer makes a surprise appearance in Kirby Mass Attack, at the end of Chapter 2 in Kirby Quest. It is possible that its appearance was meant as foreshadowing, but it was more than likely a nod to the 2005 trailer. It also makes an appearance in Kirby's Return to Dream Land.
 * Many of the screenshots, especially the Plasma one, indicate that this game may have been a 2.5D game in the vein of Kirby 64: The Crystal Shards, instead of Kirby's Return to Dream Land's 2D gameplay.
 * In the video, it looks like Kirby's model is the same one used in Super Smash Bros. Melee.
 * The Kirby GCN game that was shown off at E3 2005 was actually one of three lost Kirby games, all completely built from the ground up. Eleven years were spent making and abandoning these games.
 * The second Kirby GCN game would have been the first Kirby game in the main series where Kirby would be playable in 3D space. Apparently the game was extremely challenging. It was cancelled because it hadn't reach the quality they were expecting.
 * The third Kirby GCN game involved an animated 2D Kirby in a pop-up book setting. The copy abilities were renewed, and could power up.
 * The music in the trailer is used as boss music in Kirby's Return to Dream Land's The Arena and The True Arena. The song was used again in Kirby Triple Deluxe in the second extra stage on Royal Road before getting the Hypernova ability.