The hack is very well done. However, there are some minor mistakes.
A lot of your custom graphics are flat and have no definition. Also, some graphics are cutoff, and not to mention, there's a lot of theme clashing. There's original and retro graphics, choose one and keep it throughout the level. Also, another minor mistake is the blandness of the map. It's really flat and ugly, but I get that it's retro.
Overall, great job on the hack! I really enjoy it, keep making good hacks like this!