During the Yashiori operation against Godzilla, he's hit with artillery, trains, and collapsing buildings in an effort to weaken him enough to freeze him in place to avoid a nuclear strike being launched. Those buildings were dropped on top of him, with everything they had inside of them. Office buildings have break rooms. So Japan hit Godzilla with everything they had, including the kitchen sink!
Professor Hazama speculated that Godzilla's fins are heat vents to help keep Godzilla's blood cool—and it's the area around the dorsal fins that the the MOPs hit. Who's to say that that area isn't a weak point for this Godzilla?
Goro Maki, the scientist who was exiled from Japan and was the first person to truly discover Godzilla, left his yacht, along with his notes on Godzilla in the Tokyo Bay, allegedly committing suicide while jumping into the bay Godzilla supposedly was in. In his notes, it is shown that Godzilla can survive anywhere that there is water and oxygen present, and reproduces aesexually. This leads us to two Fridge Horror moments:
Considering that he has notes on the molecular schematic of Godzilla's cellular processes, and how it survives and reproduces, he must have gotten a sample of some sort, or maybe even met Godzilla.
Shortly before Operation Yashiori's commencement, Yaguchi spoke up about Maki's hypothetical plot to unleash Godzilla on the Japanese people, as a sort of test/revenge. Considering that he allegedly committed suicide by jumping into Tokyo Bay where Godzilla was, and not only Godzilla's humanoid traits, but how humanoids come from Godzilla's tail, and how he gains the traits of what he assimilates, one could interpret this as Maki intentionally committing suicice into the ocean so Godzilla could absorb him, and evolve properly and make more of himself.
This version of Godzilla is Nightmare Fuel, plain and simple. However, we all know that any respectable film industry who plans on making a Godzilla movie will inevitably make a sequel to pit Godzilla against a Kaiju. So when this Verse's Ebirah, Hedorah, King Ghidorah, Destroyah, Biollante or anyone else comes around... be prepared for pure, unadulterated, Nightmare Fuel.
On the plus side, this also could mean Mothra will appear. So maybe things won't be as crapsack as we fear. Maybe.
We finally know what a Shin Ghidorah would look like. There is a LOT wrong here. Firstly, Ghidorah absolutely towers over Godzilla, who is already absolutely massive in this universe. Second, the city is being assailed not just by Ghidorah and Godzilla, but by what appear to be golden spears raining down from the sky itself. It shows that as powerful as Godzilla is, as always, Ghidorah would be so much worse. And to make matters worse, while Godzilla looks like an abomination of nature, Ghidorah looks downright demonic and unnatural. It says a lot when Shin Godzilla is more of a comforting sight.
The very nature of this Godzilla's rampage isn't anger, it's because it literally has no idea where it is and why it's in pain. It's probably looking for help. Its accelerated metamorphosis keeps it in constant pain. Its skin and flesh keeps ripping apart as its body keeps growing. Even its colossal form by the film's climax resembles a walking scab that's burning from the inside. Most of its body doesn't work, like its malformed arms and enormous tail, which was likely an attempt to break off and spawn a second creature but cancelled out in favor of making a larger singular creature (Hence the semi-dead head at the tip). There`s a high likelihood that its final form is even blind, considering how random everything it does is.
The end shot is already frightening enough in its implications, with Godzilla's tail dividing into numerous smaller, humanoid monsters. However, if you note the point at which Godzilla was frozen by the coagulant...his tail wasn't like that when he was initially frozen!! In other words, this process might actually be ongoing, even while Godzilla is supposed to have been halted.