World 4-1 (Super Mario Bros. 2)
From the Super Mario Wiki
The first part of the level consists of dodging Flurries while sliding on icy surfaces and jumping over pits. At the far right there is a plant that turns into a Rocket when pulled up, which takes the player to the next part of the level. World 4-1 is notable for being the only level in the entire game without a boss, instead it has a long area filled with many enemies, with the boss music playing in the background. The Crystal Ball is lying unguarded on the ground at the end.