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The sprite of Bonk seen in the Japanese version differs from the American version. Bonk looks cuter and happier in the Japanese version while he looks bulkier and serious in the American version. In addition to that, the Japanese version includes karaoke during the credits so people could sing along with the lyrics. This is absent in the American version.
Contributed by Ophl
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In the Japanese version, if Bonk transforms into his second form he will turn into a cavewoman who can shoot hearts. In the American version, he uses a borrowed sprite from the first Bonk game, Bonk's Adventure, and instead shoots red clouds. This was possibly changed to make the game more appropriate for the target audience outside of Japan.
Contributed by Ophl