A sequel game titled Bionicle 2: City of Legends was to come out in 2004, but was scrapped for unknown reasons. The game had been in development in absolute secret, and it was only in October 2012 that someone came across the game's demo level, and uploaded a video of it to YouTube. The gameplay and visual style of this never-finished sequel was radically different, utilizing more advanced controls that let the player character produce elaborate acrobatic feats, like running on walls. The demo can be played, with a few mods, on regular Xbox consoles. No further parts of the game have ever been released, and it is doubtful that the development even got beyond this demo stage. This is probably why the game has never been formally announced and why it remained a secret for so long.
Originally, the Suva shrines were meant to be used as teleportation devices, allowing the characters to warp between areas. In the finished game, this mechanic was dropped apart from a single instance in Lewa Nuva's level.
Numerous parts of the game had to be dropped to meet the release date:
- Originally, it would have had levels featuring all of the Toa's original Mata forms and their updated Nuva forms, adding up to a total of twelve different levels, plus Takanuva's level at the end. Lewa's original form was even heavily advertised in trailers and promotional material. Most of these levels were completely cut from the released version. You only get to play as Tahu Mata, Kopaka Mata, Gali Nuva, Pohatu Nuva, Onua Nuva, Lewa Nuva, Tahu Nuva and Takanuva. Tahu is the only character to have both his Mata and Nuva forms featured.
- Originally, the village Ta-Koro would have resembled its canonical appearance more closely. In the finished game, the village looks nothing like it does in the story.
The game only very loosely follows the official Bionicle storyline created by The LEGO Company and the Danish creative agency Advance. It leaves out most of the original story year entirely and condenses long story arcs into minutes. This means that the game's story directly contradicts the official story in many places, and is thus not accepted as canon.
Although not part of the official story canon, the game did introduce two things that were later accepted into the Bionicle universe: the Mask of Elemental Energy, which replenishes the user's elemental powers, and the Nuva blast (later renamed to Nova blast), which releases the user's entire elemental power in one destructive explosion.