Fun game. The mermaid (mer-thing?) took me by surprise the first time, and I'm not sure I want to know what it was doing to me. :D
I don't 100% like the mechanic where you slow down when you pick up coins, especially since you have to go out of your way to get them in the first place. Maybe a way to drop them? Or I guess that's where being "witty" comes in, knowing when to forget the gold and run!
The game bugs out when you drown, though. You respawn with no air, and drown again immediately upon picking up a coin, and getting more air doesn't actually do anything. (Though you probably know this) The game seems to crash entirely if a mermaid grabs you mid-drowning animation.
It didn't entirely feel like a Gameboy game. Especially the five-color palette (white, black, yellow, green, and purple). The Gameboy font was a nice touch, though!
All in all, though, a fun experience. I'm looking forward to seeing the final product. :D