World 1 (SMB2)

From the Super Mario Wiki

World 1 in Super Mario Bros. 2 was the first area Mario, Luigi, Peach, and Toad ventured through. It was made into three subsections. As they traveled, the heroes were attacked by Tweeters, Shy Guys, Snifits, and Pidgits. At the ends of the first two subsections, they had to face the egg-spitting Birdo. At the end of the last subsection, they had to fight Mouser.