A "Lost Levels" styled hack in that there's very little in the way of new enemies and features, but there is a steeper learning curve and a ton of secrets to find within those levels. Don't worry if difficulty hacks scare you though, many of the early levels are still easy and there is a sincere attempt at level design and variety.
This hack improves on the original version in the following ways:
1. All Koopa Kids, Bowser, and Reznor are more difficult, keeping with the tone of the hack.
2. Lag is considerably reduced.
3. Sprite memory is improved in a few stages
4. Various bugs, some minor, some major, have been either eliminated or minimized.
5. A few minor level edits to fix bugs, such as removing Yoshi in Forest of Illusion 3 and removing the final Pokey in Chocolate Island 5, and one major level edit with Yoshi's Island 3 now featuring a faster scroll.
The hack is about 95% the same, but the changes generally make things more difficult. Unlike the original, it is not a pure vanilla hack as it takes advantage of a few patches and hex edits to tweak a few things here and there. However, it still resembles a vanilla hack in all essential ways, and those few changes ultimately allow it to play much better than the original version.
Super Mario World (U) [!].smc - SNESren (2.04)
CRC32: B19ED489
MD5: CDD3C8C37322978CA8669B34BC89C804
SHA-1: 6B47BB75D16514B6A476AA0C73A683A2A4C18765
SHA-256: 0838E531FE22C077528FEBE14CB3FF7C492F1F5FA8DE354192BDFF7137C27F5B