A refreshing and outstanding vanilla hack, that even with some issues have a great potential. Let's go:
In the same way that your game have little issues, your hack show a lot of potential. The level design is interesting, sometimes you can see a copycat
moment here and there but nothing that turn your project bad like... that bad
The puzzles were very creative and great part of the hack you give "tips" to the player (a good example is one of the Ghost Houses where you put coins in safe areas, avoiding Boo's damage).
CLOSED ENEMIES BE LIKE:
[Iceland 1 - World 3]
Already in the second stage, there is a moment of what several moles appear on the screen, causing slowdown. In other example on the first level of world 3 aka Ice World: is pretty insane dodge that Dino Rhinos. That's not a good way to increase difficulty and I recommend avoiding this type of situation.
So yeah, if you want make a hack you need take this in consideration. That's not good see that the World 3 is harder that the World 6 because, you know... ice physics don't help so much. Try to imagine a difficulty curve like a gradient: start with a bright color (easy) and every new color (worlds) the gradient become darker (hard).
[Welcome To Dinosaur Land scene]
On the first screen, the mountains are red. Nothing against red but that's very unsual, even saturated that way (was this intentional?). On the second screen there's a silly "seen seen" but nothing who will destroy the experience.
[Deep Florest 4 - World 4]
That's something very rare to see, but i believe that you need take a good
check in here. This happened when i played the level for the first time. I thought that was a bad level design choice but when i re-entered the level... the thing "fixed himself". Since the sprites don't were affected by this i presume (need confirmation, too) that the vram messed up. How that's a MAP16 bug i really don't know if No Sprite Limits patch
will be useful here, so... good luck.
"If you imitate someone, you can never surpass them."