World 6 (New Super Mario Bros. Wii)
From the Super Mario Wiki
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World 6 (also known as the Rock World) is the sixth world in New Super Mario Bros. Wii. This world features many tall mountains, high cliffs and deep caves. There are eight levels in this world, each one higher up the mountain, including two castle levels guarded by Morton Koopa Jr., and an additional airship level that takes place in the clouds above the summit. Various Mushroom Houses are also found in the world, giving the player items such as Super Stars, Super Mushrooms, and Propeller Mushrooms. On the map, there are Bill Blasters which continuously fire Bullet Bills that attack Mario and the gang.