World 1 (Super Mario Bros. 2)
From the Super Mario Wiki
World 1 is the first world Mario, Luigi, Peach, 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 Birdo, and Mouser at the end of the last level. It tends to have waterfalls with log bridges.