: Jump straight up and land on the shell. If your timing and position are correct, Mario will repeatedly bounce on the shell without touching the ground.
: Each bounce initially gives points, but eventually, you will start earning a 1-Up with every "bop". NES Cheats - Super Mario Guide - IGN Super Mario Bros Cheats Nes Infinite Lives
This is the most iconic secret in the game. It allows you to rack up dozens of 1-Ups in a single level by repeatedly bouncing on a Koopa Troopa shell. : Jump straight up and land on the shell
: You can get here quickly by using the Warp Zone at the end of World 1-2. Super Mario Bros Cheats Nes Infinite Lives