
There are also two secret levels which the players have to find the secret exits for. There is also a Ghost House in this world. Levels in this world (other than World Mushroom-Rainbow and World Mushroom-Warp Cannon) can be based on any theme. There is also only three normal levels on the main path in this world, contradictory to the five-to-six levels found in normal worlds. There are nine levels in this world and, unlike normal worlds, does not have a tower level. Notably, it is sometimes considered to be the seventh world of the game, as the numbers needed to unlock the Rainbow Course are two "7"s, but it is also sometimes considered to be preceding World 3. There are three Toad Houses in this world, one of each of red, green, and yellow varieties.

This world can be accessed by completing World 1. It is an alternative world to World 2 and thus it is optional. The background color of this world is pink.

This world has a generic design which is similar to that of World Flower and World Star. World Mushroom (or Mushroom World ) is the first special world and the seventh world appearing in New Super Mario Bros.
