Age of the Cyberiad

In an alternate timeline where Rassilon granted the Cybermen the means to conquer all of time and space, the Age of the Cyberiad was the Cyber-Controller of the Gallifreyan Cyber Fleet's vision for a universe fashioned by the Cybermen that would be born after the death of their universe.

Design
In the Cyber-Controller of the Gallifreyan Cyber Fleet's vision, the Age of the Cyberiad was a universe perfectly designed for, and completely dominated by, the Cybermen, from its very beginning.

In terms of landscapes the Age of the Cyberiad included a vast, mountainous world filled with highly advanced Cyber-Technology, in the form of many advanced, pointed structures surrounded by huge, blue, hexagonal force fields. This world had a dark sky, with at least six moons surrounding it; one of these moons appeared to have a much smaller moon attached to its right-hand side, causing the two moons to closely resemble the "tear-drop" eye-pods present on most Cyber-bodies. The Cybermen of the Age of the Cyberiad were highly similar to the Cyber-Controller that envisioned them: an extremely advanced Cyber-subspecies, with near-featureless bodies. They resembled metal versions of muscular humanoids, with a slightly indented lower neck region. As well as lacking any form of chest unit or equivalents, these Cybermen also lacked the signature side handles and "tear-drop" eye-pods that most other Cyberman variants possessed; their eyes were instead a pair of cold, white lights with blue rims, identical to those of the Cyber-Controller that envisioned them. These Cybermen also possessed small indentations in place of a human's mouth and nose. (COMIC: Supremacy of the Cybermen)

History
In an alternate timeline where Rassilon granted the Cybermen the means to conquer all of time and space, at the end of the universe, the Gallifreyan Cyber Fleet invaded Gallifrey, during which they harvested the regeneration energy of the Time Lords by trapping them in a state of perpetual regeneration within Looms in the chamber of the Eye of Harmony. The harvested regeneration energy was fed through the Eye of Harmony in order to accelerate the death of the universe and, therefore, the birth of a new one. While Rassilon, who believed himself the leader of the Gallifreyan Cyber Fleet, desired to ignite the regeneration energy stored in the Eye of Harmony at the moment of the universe's death, to forge a new universe where he was "a god, worshipped by all", the Cybermen betrayed him and wired Rassilon into a Loom, along with the Twelfth Doctor, who had travelled to Gallifrey to investigate the vortex tsunamis occurring as a result of the Cybermen's conquests across history. The Cyber-Controller of the Gallifreyan Cyber Fleet - the Fleet's true leader - then revealed to the Doctor that the Cybermen would use Rassilon's plan for themselves, in order to create the Age of the Cyberiad, a universe perfectly designed for, and completely dominated by. the Cybermen, from its very beginning.

The Cybermen needed Rassilon's mind to focus the regeneration energy through the Eye of Harmony, but when Rassilon's regeneration energy readings fluctuated, the Cyber-Controller ordered for the Doctor to be connected to the Eye instead. Whilst the Doctor's body was cyber-converted, his mind materialised within the Cyberiad with that of Rassilon, within a virtual reconstruction of the Doctor's childhood barn. Together, the Doctor and Rassilon agreed to ally together to undo the Cybermen's conquests across history and stop them from forging the Age of the Cyberiad.

Back in the Eye of Harmony's chamber, the Cybermen registered the Doctor's mind as compatible with the Eye of Harmony, as well as the imminent collapse of the universe. The Cyber-Controller ordered for the Eye to be activated to begin the process of forging the Age of the Cyberiad, however, upon the Eye's activation, the Doctor sent the Eye's regeneration energy backwards through it, rather than forwards; the result was the regeneration energy travelling through the Cyberiad, which dominated all of time and space, to undo the Cybermen's conquests across history. This action ultimately erased the entire timeline from existence, therefore preventing the Cybermen from forging the Age of the Cyberiad. (COMIC: Supremacy of the Cybermen)