Remember the line "Godzilla never does destroy Japan"? Remember Junior's Gentle Giant nature? Now the line has a new meaning due to the mess by the Futurians. The reason why Japan Takes Over the World is maybe due to Junior being a gentle giant in the movie.
Speaking of Godzilla vs. King Ghidorah, that film retroactively foreshadows the end of this one: Junior is killed then later revived and mutated into an adult Godzilla by the fallout of his father's meltdown; much like how the Godzillasaurus in Godzilla vs. King Ghidorah was killed then later revived and mutated into Godzilla by a crashed nuclear submarine.
Destoroyah was invulnerable to the military freezing weapons after his first One-Winged Angel transformation, but it's ultimately what does him in. Why? Because he'd just been super-heated by Godzilla's meltdown. His super-heated armor was rapidly cooled, subjecting him to thermal shock. He was probably reduced to a fragile wreck before he hit the ground, allowing the impact to finish him. This means that Godzilla ultimately gets the credit for Destoroyah's defeat, even though he didn't deliver a killing blow.
