Sorry for the delay I finally played your level.
I thought it was awesome but a bit too difficult overall and still way too difficult for world 4. Would you mind if we moved it to World 8?
I also love the graphics, the sunken ship section in particular looks amazing.
Here are some problems I found:
1. There is a lot of slowdown here and a bit too many enemies. I suggest removing the flying piranha plants.
2. Maybe it’s me but I found it really hard to get past this area without taking damage, maybe try adding more space to maneuver? I always find myself getting trapped.
3. It’d probably best to remove this diagonal fire ball, I found they can catch you off guard too easy if you are falling behind the screen scrolling and need to go down fast.
4. These fireballs seem out of place and add unnecessary difficulty to an already tricky situation. I’d remove these guys.
5. Like the diagonal fire ball I feel this ball and chain can be tough to react to at times when falling down this area. I suggest moving it or just getting rid of it altogether.
6. This area isn’t kind to big Mario. Raise the ceiling 1 tile higher so he doesn’t have to duck jump his way out.
Also it is way too hard to reach the pipe that leads to the secret section (blue area). I had to absorb hits in order to make it to the pipe in time before the p-switch wore off. Considering how hard the secret section is I’d just allow the player to carry the p-switch to the pipe and then use it rather than require them to race to the pipe.
7. Its fine that you require the player to keep the key till the end, but I’d at least tell the player about that requirement in a text box so they don’t waste their time getting to the end without the key. I assumed the key was for the secret exit so ignored it the first time.
8. I found this spot tough to pass regardless if the water was high or low. I suggest removing one of these enemies.
9. I feel most of these blue koopas are unnecessary, specifically the ones that walk on a 2 tile wide pipe. It looks odd and just adds more frustration to an already tough area. The phanto already provides more than enough challenge in this section.