A parallel universe (also known as an alternate reality) is a reality split off from the main timeline that still coexists with the primary universe. Parallel universes are the result of hypothetical situations in which events play out differently than in the primary universe. The BIONICLE storyline contains a number of parallel universes within its canon.
In this alternate timeline, Tuyet, using the Nui Stone, allied with Nidhiki to kill Lhikan. Tuyet proceeded to blame the deaths of Matoran she killed to appear like a countdown on the Dark Hunters and organized Toa across the Matoran Universe into the Toa Empire with herself as empress. Corrupting her empire, she eliminated organizations she believed posed a threat to Mata Nui, primarily the Brotherhood of Makuta.
In this alternate timeline, Matoro hesitated when trying to save Mata Nui and was unable to reach Karda Nui before Voya Nui fell back into place, which resulted in the permanent death of the Great Spirit. All of the species in the universe had to work together to get to the island of Mata Nui and survive. Once all species were evacuated, Takanuva set up a light barrier to keep the Makuta and their servants off the island, then became a Turaga, sacrificing his Toa power to bring about a new generation of Toa. For the next 10,000 years, the island continued to thrive as well as evolve, eventually becoming a massive city known as "The Kingdom," ruled by Turaga Takanuva.
In this alternate timeline, Energized Protodermis did leak onto the surface of Spherus Magna, and the inhabitants fought over it, unaware that their planet was being destroyed by the substance. The Great Beings noticed, and, instead of building Mata Nui to rebuild the planet after exploring the rest of the star system, they created the Toa and Matoran (having opposite statures than the main universe), sent them underground with special containers, and brought the substance out of the planet. The planet then reformed on its own, in an event known as "The Melding." The Great Beings continued to watch over the planet as the Toa and Matoran and Agori and Glatorian thrived. Makuta were also created but did not betray and remain loyal to the Great Beings.
"Reformation" Parallel Universe
In this alternate timeline, Teridax and the Makuta never rebelled against Mata Nui, and the Great Spirit was able to complete his mission of reforming Spherus Magna as planned. Mata Nui then went up north to the Valley of the Maze, apparently to restore power to where it belonged, while at least several of the beings inside him evacuated and headed toward civilization. At one point, the Makuta took over the Skrall by defeating Tuma.