I just beat both normal and secret exit, and I have a few questions regarding the secret:
How do you make that jump to the pipe that leads to the secret level? I got away with a shell-jump after not finding a better solution. Is it what you're supposed to do?
If yes, I don't think it'sa good thing in a VLDC entry. Not many casual players will think of that, they'll probably just give up.
Do you really want the boo generator to stay until the very last screen? I mean at some point it's not even about the difficulty anymore, it just becomes annoying to deal with. You can either have the generator or the other enemies by themselves in the few last screens, having them all clumped together allows you to barely move 3 tiles every boo interval. Not to mention there is a small gimmick to getting to the keyhole, so it just adds up to a lot of wasted time.
I think you overused the chucks in the normal exit level. I mean, there are 7 Chucks and the rest are just koopas. You can get away with basic sprites but if you spam chucks it just gets annoying.
I can say that I like your level overall, but I would suggest you to use multiple different sprites, or you can stay with a few but putting them to a better use other than just putting them in for the fill. Also I think you could work out a little in your 3Up Moon. I found it so easily that I didn't expect it to be a Moon but a Yoshi Coin instead. I also disliked the "NICE" in the dirt tiles, I don't think it adds anything at all, at this point you might go with full plain dirt tiles or just make some cuts or mixups.
I liked the music, the concept, the palletes, the terrain design is pretty good too and the length is ok (you might wanna reduce the timer too).
and fix this too