Despite his incredible strength, Godzilla has exhibited several weaknesses over time. Though this weakness was seemingly reckoned, early in the Showa series, he was vulnerable to electricity. Indeed, later movies would depict Godzilla as being immune to electricity, or drawing power from it.
In The Return of Godzilla, Godzilla was shown to be vulnerable to cadmium. Anti-nuclear bacteria has had an effect on him, though Godzilla’s immune system was finally able to conquer it. Later on, Godzilla is revealed to have a second brain in his back, and Mechagodzilla managed to kill him by ruining it; however, he was animated by Rodan and further movies appear to dismiss this Achilles heel.
But, the validity of this claim was highly dubious and this weak point was never exploited.
To date, the single weapon ever revealed to be genuinely effective against Godzilla was Dr. Serizawa’s Oxygen Destroyer, which disintegrated the king of the monsters down to the bone, and then into nothing. The technology for this particular weapon was lost to be able to keep it from being used again when Serizawa killed himself along with the first Godzilla.
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