World 9 (New Super Mario Bros. Wii)

World 9 (NSMB Wii) is the final world of New Super Mario Bros. Wii. The world is in space and on a giant rainbow star. Each level in the world is gated and cannot be played until a certain number of Star Coins are found. There are, just like most other worlds, 8 levels. World 9-8, the final one, has giant Bullet Bills called King Bills. These things cannot be stomped on or defeated, but can be evaded.

Trivia
World 9-7 is very hard. People thought that World 9-8 would be even harder. The thing was, it wasn't. So many people thought it was funny how the final level (9-8) was, in a way, actually quite easy!