The hack once crashed on zsnes after beating castle 2. i'm sure that won't happen that often, but just in case i whould recommend using save states on the overworld if you play on zsnes. i think it should be fine on accurate emulators, not exactly sure tho. tested castle 2 on zmz and it worked fine, that's all i can tell. however, if you see the game crashing on another level than castle 2, please tell me! i don't know how to fix the problem yet, if anyone knows how, i will update the hack with a fixed version!
Overall, pretty good. For the most part i get "traditional run'n jump" feeling when i play it, just more challenging. which isn't a bad thing. level design is pretty solid, and i can't find a single complaint about it. There are a few issues i noticed.
here i killed red parakoopa with shell i was carrying around, which i didn't know was there. i'd suggest moving it to the right and make it vertical. in Fuzzy Party i noticed small sprite tile issue, when turning around with shell. Forgotten Iceberg says that blue coins indicate slope jump, but they're not used untill second half, i feel it would be appropriate to move message here. Also, i think some music choices are a little unfitting. Castle 2 music sounds simplistic, it could fit NES-styled hack, but not vanilla SMW. I think Castle 3 music would fit a dangerous autoscroller with constant threat of death, but that's probably just my taste. other than that this is a solid hack. keep it up!