If you haven't heard, it's a totally awesome hack for Super Mario World that is difficult, but fair. More importantly though, it adds entirely new gameplay, graphics, and bosses from other games. Pretty early on you get Wood Man's Leaf Shield for a level and one boss fight is vs. King K. Rool. The hack is about as well put together as the actual original game. I highly recommend it.
You will need:
an unaltered Super Mario World (SNES) ROM.
Lunar Magic (to apply the patch)
and SNES emulator.
I linked to the English translation of the patch which I haven't played, but I assume has everything that the original version has.
If you can't figure out how to do all that, I suppose I could email you the patched file. I sort of have an inkling that it might not be entirely legal to upload it here.