These levels only edit the sprites and certain level settings, but not the physical level design.They even use glitches to make the game difficult (Invisibility on Rattle Battle and Fast Screen Push on Jungle Jinx). They may not be as difficult as the Japanese hacks, but they are still cool.
It only went up to end of world 3 (Krem Quay) so far.
http://www.youtube.com/watch?v=kS_sBcLlITM