OK, I'm finally giving feedback.
I was unable to complete the level in 25 lives, which makes this level too hard. Here's my opinion on what I saw.
--General--
I would add another mushroom about halfway through each section.
Perhaps make the piranhas that pop out of the ground an even lighter color to indicate that they don't actually hurt Mario.
--Specifics--
The jumping goomba is not necessary. I usually just end up waiting on the arch to the left, which is not fun and adds no value to the level.
You can't see where you're jumping here. Raise the blue pipe by a few tiles.
The circled fish should be moved to the right one or two tiles, as it is too much of trial and error right now. Also, the big circled section is kind of boring and could use some more content.
This part is way too hard.
The theme of the level is piranha plants in tight spaces, and this is completely different. Also, there is a slight cutoff where the red circle is.
This introductory section has too much waiting and not enough actual difficulty.
I really like the section before this, but I think the last pillar of layer 2 should be removed. With the piranha plant directly above your head, it is not intuitive that standing directly under it is the safest option.
This is just dumb. Getting through the first part is the hardest; after that it's just boring waiting. Also, the jump to the pipe marked with the arrow is extremely difficult, and I gave up due to that.
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There's a lot of things I didn't mention. That's because they were good. I genuinely enjoyed the satisfaction of avoiding all the projectiles at some points in the level. I'm just stating ways to make a good level better.