I used to buy up a lot of Famicom Disk System games and would always wind up with bootlegs mixed in. Bootlegs are usually direct copies or have only slight changes. This hack however is quite a bit different, it is a Super Mario Bros hack called Fly Mario. Fly Mario is a lot fun, you fly (swim) all the time you cannot die (unless you go off screen) and have unlimited lives, the levels are also very different.
I dumped this back in 2005 and it still doesn't seem to have made its way onto the internet so here it is.
If anyone figures out how to get past 6-1 please let me know. :)