>>19243039>Dragon/Poison>doubly weak to anything...Huh?
You have a point with the Fire-type in Water thing, though. That said, you still have those undersea volcanic ducts and whatnot to work with. Godzilla has also been shown to be capable of tunnelling through the Earth's mantle/outer core at high speeds, so he probably has some extra heat affinity.
We'd need a separate Godzilla type to catch all of his elemental attributes properly. Like the time where he mind-crushed the world's strongest human psychic. Or the time he used magnetic attacks. Or the time he flew.