World Mushroom (Super Mario 3D World)
From the Super Mario Wiki, the Mario encyclopedia
World Mushroom (called Mushroom World on Miiverse) is the second special world and the tenth world in Super Mario 3D World. It sits adjacent to World Flower and consists of remixes of previous courses; they are harder versions which may be set at a different time of day, be a speed run course or have additional objectives. It is unlocked after clearing Cosmic Cannon Cluster in World Star. This world contains seven regular courses and one Mystery House. It is the first world not to contain any stamps within its levels.