At the base of the Geosynchronous Energon Bridge, far beneath the surface of Cybertron, the Energon Bridge Guardian lies ready to defend the Bridge against interlopers. A huge and ancient machine, it possesses sweeping energy beams and homing missiles of unknown vintage. It does have one glaring weakness—for reasons known only to its creators, after each firing cycle it opens up, making its own power core vulnerable.
As Starscream, Thundercracker, and Skywarp attempted to reactivate the Energon Bridge, they reached the Guardian and attempted to use a detpack to infuse it with Dark Energon. The Guardian activated and started firing rockets at them. The trio managed to evade its firepower long enough to use their own weapons to blast its power core, eventually destroying it. Their job done, the three Decepticons escaped through a passage to the surface to watch the Energon Bridge reactivate.