>>149549032
What's interesting is that it feels like it was an American toy trend, but it's even on the Takara concept art for the toys(for those unaware,the TF design process tends to be the US side coming up with a concept and some early sketches, then the Japanese side actually finalizing the design and engineering it)
...but then I realized Takara actually handles the TMNT license in Japan for Playmates, or was for a long time, so it's possible the TMNT mouths was basically them leaning into elements of those because they were popular internationally. They knew TMNT sold and implemented bits of that