The idea of illusion is a tricky thing to work with, and just simply changing the graphics of things could get a bit frustrating. So i see you tried going with a more plain style to compensate, reducing the challenge to the player, that will now just focus in discovering what each thing is given it's behavior. It's a bad thing. Is workable, but could be better.
What i suggest is, try to incorporate the illusion in a more natural way, something that could interact directly with the landmass. Simple example: make a falling sprite plataform with ground tiles, you can easily blend it to the scenario, gives player time for reaction, is unexpected while not being unfair, and making the terrain more engaging to walk further the screens. To avoid cutoff, you can make something using the objects going behind the sprite to fix any problem with it.
Wooden chained plataform is another good sprite to use, you can achieve great results with it.
EDIT: You can also try making something with "impossible structures" sort of optical illusion in mind, it would be interesting too.
Not saying the level is looking bad by any means, it's just it could improve greatly and be spot on compared to same thematic levels. I like your work, so i hope you take good ideas out of these lines. Good luck with your level.
Also, one problem i found about the boos: you can spin-jump into them, but not the other spikes, that could lead the players to think spikes are spinjumpable, even with the illusion idea in mind.
Originally posted by Golden Yoshi
As for the 30 coin challenge, I've come up with a way to have it lead to the secret exit.
Can i venture a guess?