Time for a short review:
First of all I love your art style, your background, overworld graphics, enemie graphics and that player graphic is super cute as well. Actually everything is looking super nice.
The overwotld is neat, loving all of the decorations, also how long are you planning to create this hack, one world or several worlds with different themes?
However I must say that I don't always like the level design, especially the first level could use some work. The palette could be a bit better (escpecially the foreground should be a bit darker, since it's a night-time level). Also was there another way to the autoscroll section, than by going into the bonus room (they were all way too easy to find), there wasn't anything if I continued walking right? Also as a small nitpick it would be better if you come out of pipe, after going into a pipe. The autoscroll section was okay-ish but a little bit short and bullet bills were most of the time the only enemies.
The ice level was by far my favourite one (level design + graphics). It had lots of variety and there's just one thing I dislike. On screen 5 (yep I'm using lunar magic, but just to better discribe would you could improve) the jump from the second grey platform was pretty hard compared to the rest of the level.
The desert level was also a neat one, I however think i would be better if the pyramid would be build of slopes. And the quick sand being no harm anymore if you've got a star is pretty odd. But the level was pretty fun, with some hidden extras (1-ups, powerups...) to find.
Can't say a lot about the cave(?) level, it was ok-ish the design was nothing special but it wasn't bad either. There could have been a bigger variety of enemy types.
This hack definitely has a lot of potential and I really liked playing it, can't wait to see more of it in the future.
Edit:

This is just too cute

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