I watched the speedrunners beat this game by doing the Ending Glitch. So I decided to give a try. I found a tutorial how to do the glitch and it took me few times to get it right. I been practicing for 2 hours to do this right you have to be patient not to rush it.
To do the glitch right you have to position the Koopa's shells many people do the glitch differently and this one i did is easier. I'm not a pro on Super Mario Bros. 3, in my opinion Super Mario Bros. 3 is harder than Super Mario World.
To get to the ending it doesn't work for SNES version.