Sorry for the late reply, I was very busy these days. But now I'll give my proper feedback about the demo.
The first thing I have to say... The presentation and the graphics are the best part of the hack. You combined very well various assets, as seen in various stages of the hack.
About the level design, I think it can improve even more. While in stages like that one from the mushrooms and the swamp are very nice, I think you could tweak a bit more some like the Blue Grotto. Some stages I found way too easy, while others were a bit more hectic. The curve of difficulty is a bit odd, if you ask me.
Also, in the forest exit, you mention about climbing tree branchs and the rest of level doesn't use it anymore. It's not bad, but weird. I think it would be very nice if you expanded this gimmick.
The priority in the pillars of the forest castle looks so odd. And kinda annoying, tbh.
In general, the hack is okay, but needs more adjustments in the level design. I definitely see the potential there. Good luck!