Subcon, the land of dreams, is the setting of Nintendo's many renditions of Super Mario Brothers 2 (which also includes Super Mario All-Stars, BS Super Mario USA, and Super Mario Advance). The story goes that one day while out on a picnic Mario, Luigi, Toad, and Princess Toadstool came across a mysterious staircase upon which, at the top, was a door. The door was the entrance to Subcon, a place where the evil Wart had imprisoned the local natives and was repopulating the realm's seven lands with monsters from bad dreams. The first six worlds are split into three sections with each section being guarded by a creature named Birdo who guards the crystal ball that opens the eagle's head passage to the next section of the world. World seven is two sections long and contains Wart's castle. Also, while the Mushroom Kingdom is mostly horizontal, Subcon has many vertical segments that are accessible by vines. Other natural landscapes include green hills, waterfalls, and falling logs.

Subcon is also known for its many vegetables that grow in the wild. Turnips are the most common, but other kinds of produce include strawberries and peppers. Ripe vegetables are large and have a smiley face on them, while unripened ones are small and undergrown. Plucking five ripened veggies from the ground in a single level freezes time for several seconds. There are also wild cherries that float in the air, and snagging five of them in a single level summons the mighty Starman. And as if all of these crops weren't enough, magic potions also grow throughout the land, and tossing one of these potions to the ground opens a door to the realm of Subspace where mushrooms and coins can be found.

At the end of the game it is revealed that the land of Subcon was actually part of Mario's own dream. While this should mean that the land and its inhabitants do not really exist, many of the monsters in the land, such as Birdo, Shy Guy, and Bob-omb, have been seen in later Super Mario Brothers games. One can therefore assume that while the land itself does not exist, the baddies in it do and were present in the dream because Mario was familiar with them in the real world. Wart, on the other hand, has never been seen again and therefore probably does not exist outside of Mario's dreams.