World 7 (New Super Mario Bros. Wii)
From the Super Mario Wiki
World 7 is the seventh world in the game New Super Mario Bros. Wii. The area is sky themed and contains many clouds and high cliffs. However, it does contain several unique enemies in its stages, and is highly abundant in items (mostly Ice Flowers, Fire Flowers, and Propeller Mushrooms). Ludwig von Koopa is the boss of the world, and the players will see him on the roof of a fort he built with traps. The Enemy Course in this area contains a single Lakitu that throws Spinies. There are also various Toad Houses, including two yellow ones that contain Stars, unlike all the other worlds that have only one yellow Toad House at the most.