Godzilla has often been called a walking nuclear reactor. Here, the reactor has gone critical. If he implodes, he turns Japan into an uninhabitable ghost town. If he EXPLODES, he destroys the entire planet. Not to mention the side-effects on Godzilla himself, who has just about gone Ax-Crazy from the pain he's in. The red on his face and body does not help.
When Godzilla begins melting down at the end of the final battle, his skin literally begins to melt. A close-up shot near the climax of the final battle shows off one of Toho's first uses of CGI, a pretty convincing example of it at that... and it's of Godzilla's flesh starting to drip off his skull!
Destoroyah. To quote James Rolfe, "He looks like the goddamn devil!" It doesn't help that his juvenile forms look like a cross between a Xenomorph, a crab, and a scorpion, or that he's able to use the same horrific ability as the Oxygen Destroyer.
Then you get into his origin. He's a pre-Cambrian life form awoken and mutated by the Oxygen Destroyer (see above, also where he got his name), the only weapon to ever permanently kill a Godzilla. Essentially, Destoroyah is the living embodiment of everything Dr. Serizawa feared about his creation.
Destoroyah's arrival in his Perfect Form is just as shiver-inducing as it is awesome; after being blasted into an oil refinery by Junior earlier on, Destoroyah, who had absorbed Junior's DNA after biting him in the chest, manages to evolve to a state where he gains an internal skeleton, allowing him to take on his iconic bipedal stance. Just as Junior and Godzilla finally reunite, a wave of energy erupts from the refinery, causing it to be blown completely apart. As the flames rage and the dust clears, Destoroyah stands tall, his wings outstretched, accompanied by the deafening brass sting that commences his theme, plus a low angle shot that fully shows off his demonic appearance.
Even his roars are terrifying. With the high-pitched shrieks and wailing, he sounds as absolutely demonic as he looks, as heard here.
The entire sequence where the juvenile Destoroyah attacks Yukari is this. The poor girl is cornered in her car by the creature, which attacks and damages the vehicle in a mad frenzy to get to her. This jams the car doors, leaving her unable to get out. She barely avoids being maimed, blasted, and having her face eaten off multiple times, and if not for the timely arrival of G-Force, she would have most certainly been killed.
The fact that Destoroyah is awakened by the Oxygen Destroyer meant Serizawa's fears had came true. To the point he strips several fish to the bone in the aquarium scene.
Also that Destoroyah is the living embodiment of the only weapon to ever permanently kill Godzilla. No last minute radiation, no magic, no nothing, that Godzilla was dead. And now that weapon is a giant monster. Imagine if the Tsar Bomba gained physical form and started walking around.
The Indian version of the movie, retitled "Last Godzilla", basically turns the film into a goddamned creepypasta. The movie is re-edited, sometimes rescored, Destoroyah is randomly given a new, even more terrifying roar, and to top it off, Junior's resurrection is cut out entirely. The ending freeze frames on a sobbing Miki and slaps up a gritty, in-your-face (and in English) "THE END".
, his wings outstretched, accompanied by the deafening brass sting that commences his theme, plus a low angle shot that fully shows off his demonic appearance.