It's another one of those reviews from you know who... ME!
Here's your grade for your level.
Now I'll give the feedback.
Gameplay: 90%
Pros.
Good job using the clams as gimmics. I like how you made them an instant death if you got caught.
I also really liked how you made the whole level full of multiple diverging paths. It helped keep me interested.
The special coins were well placed in harder areas to reach (except for the last one)
I liked how you made many cheep cheeps spawn, but they didn't come out too fast, as to impede any way of swimming forward.
Cons.
Instead of saying that you shouldn't jump on enemies because the player is in the deep ocean, you could've said that the enemies were poisonous and they would hurt you, because otherwise it doesn't really make sense why a goomba without spikes would hurt you.
The last special coin should've been harder to obtain.
Some areas needed more coins. I will show one area.
Graphics:84%
(I am going to be nit picky about this, but I won't take off major points for small mistakes)
Pros.
The Graphics fit well together. I liked how you incorporated vanilla graphics to fit into the level.
I smile upon the variety of npc usage. It made the level more interesting.
I like the transparency of the lotus volcano.
Good usage of the holes in the rocks for spawning cheep cheeps.
Cons.
The outlining was mixed between dark grey and black. Either you should've used only black outline or grey outline.
I suggest that you use some tile variety though. It gets a bit boring. Same goes for the backgrounds.
It's kinda hard to see the toad's eyes. Next time try to make them more visible, because I thought they had no eyes in the beginning. :p
The boat with the star floating over it should've looked more wrecked. It would fit the sad music theme better.
I suggest that you use one type of color for the block, instead of darkening it. Also the bottom corner block needs to curve.
Ambiance and background: 100%
I have nothing against anything with the background or the ambience I feel like the night sky and ocean bottom fit well, and the music helped keep the sad slowness of the level together.
Overall, this was a well made level that needs a few tweaks. I would say that it should go into the pretty good section.