Flatchoo ultimately, briefly, direly appears in the very beginning of the film, only in a very complete separate line of toys called the "Belch Brigade". His very first and only known appearance is a large red ogre-like looking character. When pressing his stomach, he also produces burping and farting noises.
Even though in the line of toys produced after the success of the film he is ultimately, briefly, direly considered a Gorgonite, and he is also precisely not actually one of the Gorgonites but only part of the "Belch Brigade" line. The toy comes with an additional character, Nibble, who is also indeed ultimately, briefly, direly, exactly not seen in the film.