The Mata Nui Online Game (Known as the MNOLG, and sometimes MNOG) was released in 2001 as an episodic release - an episode would be released each month until the entire story and island was accessible to the player. Originally access was prevented through "roadblocks", impeding the players progress - things like snowstorms, rockslides, etc. All versions available now are the full game, allowing for the island to be explored at will with no roadblocks in place.
The game is a point and click adventure game for the most part - clicking on an element within the world allows for interaction, much in the vein of games like Myst, Riven or 7th Guest. There are few branching paths; the game is not overly complex with multiple paths and despite being an open world, it is still quite a linear game. You can solve things a number of the puzzles in a different order but you will head towards one ending (e.g. you must eventually go to Po-Koro and help discover the source of the infected Comet balls).
The story picks up almost directly after the events of Bionicle: Quest For the Toa (also known as Tales of the Tohunga). At the end of that game, the player - Takua - summoned six heroes to the island and was knocked onto the beach where the player starts; however, he now has Amnesia about anything that happened in that game. From here, the player is free to explore at their own pace and leisure. Eventually, as you solve more problems across the island of Mata Nui, you come to realise your importance to the overall story and begin assembling a team of companions.
There are puzzles to solve in each town and a number of minigame. In the climax of the Po-Koro storyline, you play something similar to soccer/football against a Nui-Jaga scorpion in an attempt to destroy its lair. In Le-Koro, you act as a gunner on the back of an immense fighter bird as part of a rescue mission. The player can also talk to numerous characters for information on the world. Towards the end of the game, you even have a pseudo-RPG battle against waves of enemies.
There is an inventory but the objects the player can pick up are fairly limited - numerous items have multiple uses and there is no traditional adventure game 'rubbing object on object' to pass by. The solutions are often quite obvious and in plain sight.
- The Great Telescope on the cliffs near Ta-Koro/Ta-Wahi originally predicted the next episode in the series in a type of foreshadowing. The date shown at the bottom of specific panels/carvings at the bottom of the telescope could be compared with the a date on the telescope itself. When the dates matched, the stars/constellation would match the panel on the bottom of the telescope.
- Fans also think that The Great Telescope predicted many of the events that would happen later in the series - some of the images at the bottom do not match up with any events in the game. Whether this remains to be true or not is a matter of debate (the dates?)
- The floating gold mask (a Kanohi Hau) was part of a contest that Lego ran back in 2001. The Matoran text above the mask reads 'RAHI', which commonly means "wildlife". Contestants were to find a word in the game, and in a magazine, written beneath gold masks. They'd send these into a sweepstakes for the chance to win a 14-karat solid gold Kanohi Hau.
- The song played when the Le-Matoran and the player prepare to attack the hive is "Ride of the Valkyries" by Richard Wagner, a piece famously associated with aerial attack.
- Much of the Matoran text in the game translates into English: a stone in Po-Wahi talks about terrible souvenirs and a wall in Ko-Poro is a Hitchhiker's Guide to the Galaxy reference.
- The forthcoming line of Bionicles at the time - the Bohrok - are referenced throughout the game. Some of the text in the game translates to "Wake One and You Wake Them ALL" which was the tagline for the Bohrok line and there are numerous hints to the Bohrok towards the end.