''And now... my Mecha. It’s not only Godzilla's equal... but his superior. The Apex Titan of my own hand. It's time to show the world what you can do.''

— Walter Simmons, as Mechagodzilla is activated (Godzilla vs. Kong)

A robot duplicate of Godzilla, Mechagodzilla was constructed in secrecy by Apex Cybernetics to end the reign of the Titans, and was piloted by Ren Serizawa via a neural connection between the mecha and the skull of King Ghidorah which Apex had acquired from eco-terrorist Alan Jonah. In 2024, Apex organized a mission with the scientific organization Monarch to lead an expedition into the Hollow Earth to find an energy source capable of powering Mechagodzilla in the wake of Godzilla's sudden rampages. When the energy source was recovered, it was used to activate Mechagodzilla while Godzilla and Kong battled in Hong Kong. However, the untested power source allowed Ghidorah's consciousness to possess Mechagodzilla, causing it to quickly break free of Apex's control. The rogue mecha killed its creators and tore its way out of the Apex facility, bursting free from beneath Victoria Peak Mountain just after Godzilla defeated Kong. The mechanical monster set its sights on its organic nemesis and bombarded him with its plethora of weaponry and empowered physical attacks, easily overpowering Godzilla. Just when Godzilla seemed outmatched, Kong came to his enemy's rescue, helping to turn the tide. By cooperating, Godzilla and Kong were able to triumph over the Ultimate Destroyer when Godzilla charged Kong's axe with his atomic breath, allowing Kong to slice Mechagodzilla apart and end its rampage.