The great thing is that there's literally no context for Godzilla to be in Revenge of Shinobi and the he's the boss of a level that's set entirely on a huge PLANE.
When this game was new I don't remember anyone who even bothered trying to formulate a strategy or anything since he was practically impossible. People would just save up as many lives as possible and then use 2 or 3 suicide attacks which would usually kill him outright.
I actually beat Revenge of Shinobi about a year and a half ago. While I didn't use any sort of infinite shuriken or lives option, I did not have beaten it on a single credit, so I'm not that hardcore.
Most people I remember back then just got good at the game without using shurikens. I was able to beat it after learning the overall strategies. Like i said, the way I learned the game was to beat Godzilla using the suicide power thing and just try to have as many lives as possible at that point. I remember being impressed at how you could get a "bad" ending.