Hello,
I tried and tested your hack today. Unfortunatly, there is a lot of problems with it...
First, Marix dies in the title screen. Then, we should be able to save after each level (because it's a Kaizo hack). Furthermore, in the first level, you could add some coins to help the player know where to shoot the shell (like in the last jump, put a coin next to the wall...). Some other level would benefit of coins indicator.
In level 3, when you do the slide jumps, the third one is really tight, you should maybe cut the corner larger than it is.
The level 5 is such a pain in the ass loll (you should rename it 'High Pain" instead of "High Plains" hahah), and you have to do all the level again to have the secret exit... witch is not a good idea. At least, we can keep the yoshi at the end! Plus, there is some problems with the level tiles: one corner of the "column" is empty, and putting the blue plants of these columns as munchers is kind of weird... you should just put munchers instead I think.
In the ghost house, the disco shell part is really long and not really fun.
Finally, I beat "Fly Test", but your path is not good on the Overworld, so Marix gets the f*ck out when you beat the level loll
I put some other problems I had with your game in this low-quality (sorry) video: https://youtu.be/Rd4gGXe6Xqs
But, there's some things I liked about your game!
Level 1, 2, 4 and the fortress were really fun! The gameplay was cool. Those were the best levels in my opinion. There's a couple of nice tricks in the hack so far. So, there is a potential if you keep working on your hack!
Hope this will help you.
Have a good one!
-TonY-
(PS: sorry for my bad english... I'm French Canadian)