Mystery Box

Mystery Boxes are found in Super Mario 3D Land, and give reward for completing the challange in it. They are mostly found on maps, but can also can be found in some levels too.

Golden Mystery Boxes
Gold Mystery Boxes are only found on the map, and give you lots of good rewards with out having to complete a challange. These ones usually contain more than 1 Star Medal.

A very rare gold mystery box in world 1 contains 2 Star Medals, 15 Super Leaves, and a P-Wing.