The mermaid moves faster if you are behind, and actually you can full screen on PC with F4! What is it you don't like about the sponges? They fly around too much?
Oh snap, didn't know about the F4, thanks! Sharks have a tendency to hit a sponge and then move diagonally to where you are, additionally there are way too many of them at random intervals preventing you from dodging; kills the fun quickly. Shark hitbox seems janky AF as well, hair and forehead seems to trigger a loss on their first run. Cajun fish should follow the same logic as the other specials.