Why such a specific question?
In any case the only instances coming to mind, where there might be a shot of Godzilla stepping in mud, is the end of Godzilla vs. Biollante where they attempt to raise Godzilla's temperature or the opening of Godzilla x MechaGodzilla when he makes landfall. But I'd have to re-watch both sequences to see if such a shot exists. I'm leaning more towards Godzilla vs. Biollante.
"'Nostalgic' does not equal 'good,' and 'standards' does not equal 'elitism.'" "Being offended is inevitable. Living offended is your choice."