These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fanon Discontinuity: Neither the Disney company, nor the majority of fans recognize it as "canon". In fact, this movie is most often cited to illustrate the "Disney DTV sequels are animated fanfiction" argument.
Fridge Horror: Mermaids are fish from the waist down, which implies they fertilize externally. For all of Ariel's life, she probably understood having children as a matter of squirting into a hole. Now imagine her reaction to going through humans' messy and painful way of doing it.
Idiot Plot: The Movie could have ended faster if Ariel had just told Melody why she couldn't go to the sea.