Reign of Shadows contains canon BIONICLE info.
"Reign of Shadows" is not an official name
The Reign of Shadows, also known as Teridax's Reign, was a period of conflict between inhabitants of the Matoran Universe and Makuta Teridax and his forces after the Makuta took control of the Great Spirit Robot.
Immediately following Mata Nui's awakening, Makuta Teridax enacted the final phase of his plan and took control of the Great Spirit Robot, using his newly-acquired powers to announce his victory across the entire Matoran Universe. To ensure that Mata Nui could not interfere or fight back, Teridax imprisoned the former Great Spirit into the Kanohi Ignika and launched it into outer space, unknowingly towards Bara Magna.
With Mata Nui expunged from the Great Spirit Robot, Teridax set about crushing the remaining resistance fighters to ensure his reign would continue unimpeded. First and foremost, he eliminated all remaining members of the Makuta species save for Miserix, convinced that they would at some point betray him if left unchecked.
Conjuring legions of Rahkshi and recreating the Visorak species, Teridax would later use the creatures as instruments of his will, driving the Dark Hunters out of Odina and seizing their base of operations. Rahkshi squadrons were distributed throughout the Matoran Universe, tasked with terrorizing the Matoran and any surviving Toa. Now aware of the Order of Mata Nui's existence, Teridax obliterated the Daxia dome, killing a number of Order agents and scattering any organized resistance. With the Toa divided and with only a handful of capable warriors taking refuge on Stelt and Xia, Teridax cemented his victory by appointing his long-time servant Ahkmou as "Turaga" of Metru Nui. Those who opposed Teridax were forced into hiding due to the extreme number of Rahkshi and Exo Toa in the Makuta's army.
Over the course of the ensuing months, a number of coups were attempted in the hopes of reclaiming the Matoran Universe. With Toa Helryx and Miserix imprisoned within the Core Processor, a rescue was mounted by Axonn, Brutaka, Toa Tuyet, Kapura, Hafu, and Tren Krom, who had possessed the body of Toa Nuva Lewa. Freeing Miserix from his prison and exposing a bank of machinery, Helryx was the option to damage the operating system and permanently debilitate Makuta Teridax, dooming the Matoran Universe. Divided, the group broke into a skirmish, with battle lines being drawn and Helryx attempting a Nova Blast. However, the timely arrival of Artahka brought the battle to a standstill. With Tren Krom's consciousness returned to its original body, Teridax made his presence known before teleporting the entirety of the resistance group out of the Great Spirit Robot and into the vacuum of space. While Lewa Nuva was able to summon a bubble of air to save his cohorts, the group was forced to drift towards Bota Magna.
Following the reassembly of the Prototype Great Spirit Robot on the surface of Bara Magna, Teridax sensed the presence of Mata Nui and decided to eradicate his nemesis once and for all. Using the jet propulsion systems built into the Great Spirit Robot, Teridax set the Matoran Universe on a course towards Bara Magna and commanded his Rahkshi armies to converge on the southern regions, ready to be deployed to the surface.
Secretly joining the vast contigent of Rahkshi were Toa Nuva Tahu and Takanuva, who accompanied the creatures onto the land of Bara Magna. Teridax and Mata Nui did battle as the Bara Magnans faced off against the Rahkshi and their Skakdi allies. With the help of a contigency plan in the form of the Golden Armor, Mata Nui managed to shove Teridax into the path of the incoming moon of Bota Magna, ending the tyrant's life and simultaneously ending both the Battle of Bara Magna and the Reign of Shadows.
- While Reign of Shadows is actually the title of the story serial that details efforts to resist Teridax's rule, the phrase has been used by fans as a name for the period of time it took place in.