World 1 (Super Mario Bros. 2)
From the Super Mario Wiki
World 1 (known as Chapter 1 in Yume Kōjō: Doki Doki Panic) is the first world Mario, Luigi, Princess Toadstool, and Toad venture through in Super Mario Bros. 2. It is divided into three levels and inhabited by Tweeters, Shy Guys, Snifits, and Pidgits. At the ends of the first two levels, the heroes have to face the egg-spitting Pink Birdo, and Mouser at the end of the last level. These levels tend to have waterfalls with log bridges.