A brand new Godzilla suit was designed for this film and some slight alterations were done to its overall appearance.
It is controlled by Ren Serizawa, the son of the late Ishirō Serizawa, through the neural networks from the skull of a severed Ghidorah head, but is hobbled by its power supply's limitations.
Of course, the real Godzilla has to battle his new foe, and so one of the great Godzilla antagonists was born.
If you want to really know what Godzilla is all about, then make sure to check out the original Japanese cut of the 1954 monster movie.