Well, this is a little terrifying. Very impressive designs as always. Based on the name, am I correct in assuming Neptune's Maw is a water-themed dungeon?
In my opinion, the border between the dark blue areas on the top left and right and the lighter blue areas below them is a little too much of a straight line. Unless there's some sort of animation effect only visible in the game itself, you might want to make those borders a bit more ripple-like or diagonal.
Also, I'm not sure what the green spire in the middle of the screen is. Maybe I'm missing the obvious here, though.
By the way, what's up with poor Reyson? That expression on his face is more than a little concerning. He must have seen some really bad stuff recently.