Alternate Character Interpretation: While Destroayh is near universally considered one of the most violent kaiju in the franchise, the reason behind the violence is left vague. Some think that it's simply a case of Destroyah being a genuine sadist and taking pleasure in the devastation it causes. Others interpret Destroyah's actions as a Non-Malicious Monster that is acting on instinct, and lashing out at everyone after it/they had been harmed to remove threats to itself.
Crowning Moment of Heartwarming: After a Tear Jerker conga at the end, we see that Junior absorbed his father's radiation (saving the world in the process) and has matured into a fully grown adult as the next Godzilla. Our little prince we've seen grow up over the last few movies has taken the throne as the new king.
Ensemble Darkhorse: Though he's the main villain, as a Kaiju overall, Destroyah has quite a large following thanks to this movie. Many saw him as an insanely dark and cruel monster that gave Godzilla one hell of a show.
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.
In the original film, Serizawa tells Ogata to be happy with Emiko when he makes his Heroic Sacrifice. In this film, she did not marry him after the events of the original and is most likely suffered from Survivor Guilt when she felt she had no choice but to reveal the Oxygen Destroyer.
Serizawa's fears of the Oxygen Destroyer has become a reality now that the Oxygen Destroyer has awaken and mutated Precambrian life-forms whose powers derives from the weapon that killed the first Godzilla.
Memetic Mutation: DESTOROYAH!!! In the Godzillathon review of this movie, James Rolfe always says "DESTOROYAH!" whenever he addresses him. He even does this in the AVGN episode "Godzilla".
Nightmare Fuel: The film surprisingly has an amount of nightmare fuel in the film. These include:
The side-effects of Godzilla melting down. The red on his face and body does not help.
Destroroyah's unnerving appearance and his Hell Is That Noise roar. Does not help that his final form looks like "the goddamn devil".
The fact that Destoroyah was awaken by the Oxygen Destroyer meant Serizawa's fears had came true. To the point he stripped several fish to the bone in the aquarium scene.
Junior's death, and Godzilla's failed attempt to revive him. The music for this sequence is appropriately titled Roar of Sadness. Also, Godzilla's death.
Hell, even the events leading up to Godzilla Jr.'s death was a Tear Jerker when you really think about them. Up until the final battle, Godzilla was desperately in search of his son, following him from location to location. Godzilla apparently KNEW he was dying, and like any father on his death bed, wanted to see his son one last time. And just as they're about to embrace, Destroyah breaks up the reunion and kills Junior. No wonder Godzilla got so pissed and started beating Destroyah so savagely. Godzilla had nothing left to lose.
Emiko Yamane post-1954. In the original film, she was one of the witnesses of the original Godzilla. The film heavily implied she is suffering from Survivor Guilt after what she did: Reveal the Oxygen Destroyer. Not only was she unfaithful to her fiance, but Daisuke told her to be happy with Ogata. But considering her surname, the film also implies she didn't marry Ogata either. Poor woman...
They Wasted a Perfectly Good Plot: A scene featuring Godzilla giving Destoroyah a No-Holds-Barred Beatdown as dies was removed because it lessened the impact of Godzilla's death, though it's still pretty satisfying to watch. That ending was shot as a dupe and never meant to be used. Wires and filming equipment can be seen in many of the shots, betraying its hastily put together nature.