Transformers: Cybertron brought the “Universe Trilogy” to a close, adding a final installment of a thematic ally unified toy series. Beginning in 2005, the series came full circle within the Trilogy by abandoning the variety of themes and features in Energon by returning to one series-wide gimmick, like Armada.
In this case, the feature was the Cyber Planet key. Each toy came with a translucent plastic “key”, which could be inserted into the figure to activate some spring-loaded special weapon or feature. On the back of each key, Hasbro (but not Takara) tampographed a four-letter alphanumeric code, which could be entered on the official Transformers website to unlock background information or pictures about the corresponding character.
The design of the key also alluded to which planet the character came from. Each of the six planets in the fiction had a corresponding key type, and its inhabitants generally fit an certain design ethic: Earth Planet featured a number of less fictitious cars and jets, recognizable by some real-life analogue; Speed Planet inhabitants were all exotic science-fiction racers with translucent plastic wheels; Jungle Planet characters were robotic beasts looking somewhat like the Beast Machines Maximals; the few Giant Planet toys were meant to look like huge construction equipment, and included “helper” Mini-Cons for tasks the main character was too large to complete. Toward the end of the series, two less-defined planets were introduced: Planet X, Unicron's minions, and Cybertron Planet, a mishmash of fictional designs.
Despite this rigid structure, several retooled toys from Armada found their way into Cybertron, often with their Mini-Con action features altered to activate with the Cyber Keys. Other than this, Cybertron contained a series of redecoed Armada Mini-Cons sold in “versus”-style two-packs. Like many contemporary series, Cybertron included redecoes of almost every new mold it introduced. It also introduced the concept of the “Legends Class”, small, simplified versions of the main characters sold at a $5 price point.