Far in the northern regions of the planet, it is known for being cold and inhospitable, and the sea route between it and the Central Continent is blocked by a dangerous region of electromagnetic storms known as the Triangle Daras. It is home to the Guylos Empire, and once was home to the Dark Zoids (such as Deadborder and Heldigunner). Bizarrely organic and glowing an eerie green—which, in some versions of the story, had a detrimental effect on vegetation and terrain—they were powered up by an ore called Deochalcum (possibly a play on Orichalcum).
In the early Japanese story, Nyx remained mostly mysterious: its first mention was back when King Helic scouted it during the days of tribal warfare, and then not by name. He led its inhabitants and their strong Zoids back onto the fighting Central Continent factions, using this attack from a foreign enemy as a last-ditch way to make them realize they had to work together. The Helic Republic was formed soon after, the strange northern Zoids disappearing along with their pilots who, being used to Nyx's cold and dark environment, found a unified front and the Central Continent's summer heat more trouble than it was worth). Helic's son (Helic II, aka the President) took over the Central Continent's rule.
During the war between the Republic and the later-formed Zenebas Empire, Zenebas and his army fled to the Dark Continent after the deployment of the Ultrasaurus forced them to seek Guylos' assistance. The Zenebas armies were rebuilt with Zoids such as Dimetrodon, Wardick, and eventually Death Saurer, and the conflict between the two sides continued until Mad Thunder's unveiling. Guylos saw this as the perfect opportunity, striking while the Republic was weakened and Zenebas near defeat to kidnap his Zoids and army as his own.
More of Nyx was then revealed, as the Republic went after the mysterious Dark Zoids that attacked the Central Continent. It was full of nasty volcanic terrain, twisted complex mazes of ashen valleys (known as The Devil's Maze) proving difficult to navigate and leading to drawn out battles. The Republic pushed on to what appeared victory by King Gojulas, but the meteor disaster in ZAC 2056 cut the war violently short. In Nyx's case, large portions of the continent tore apart, sinking into the ocean, and the Triangle Daras expanded. The rest survived, however, and the Guylos Empire's capital moved from Chepin to Valhalla until Prozen destroyed it by self-destructing his Death Saurer.