Godzilla is very resistant to heat, he swam through magma, and was exposed to heat generated by nuclear explosions many several times. Despite his incredible strength, Godzilla has displayed a few weaknesses over the years. Early in the Showa series, he was vulnerable to electricity, though this weakness was apparently reckoned. Indeed, later films in the Showa series would portray Godzilla as being immune to electricity, or even 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 eventually able to overcome it. Later on, Godzilla is revealed to have a second brain in his spine, and Mechagodzilla was able to kill him by destroying it; however, he was revived by Rodan and further films seem to ignore this Achilles heel.
It was also suggested by the character Yuki in Godzilla vs. SpaceGodzilla that Godzilla has a soft spot under each armpit. However, the validity of this claim was highly dubious and this weak point was never exploited.
Godzilla’s sheer bulk has also been depicted as a disadvantage, making it difficult for him to keep up with the more agile Megaguirus, who was able to outmaneuver him as well as forcing Godzilla to have to rely heavily on his endurance. Also, while he has an endurance level beyond measure, his enemies usually counter by trying to crush and batter him.
Godzilla’s biggest weakness is his own atomic breath. This was demonstrated when Mothra used her scales to reflect Godzilla’s atomic breath back at him, forcing him to retreat. Aside from his own weapon being turned against him, Godzilla Earth struggled to defeat Ghidorah due to the creature’s ability to ignore the universe’s laws of physics. This unusual situation allowed Ghidorah to bypass Godzilla’s shield and prevented the King of Monsters from attacking.
The gills on Godzilla’s neck appear to be a weak spot, first demonstrated when he smashes through the Golden Gate Bridge after being hit there by missile fire. The two MUTOs were able to draw blood from Godzilla by stabbing his gills with their claws.