World 6-3 is the third main level in World 6 of New Super Mario Bros. 2. This level contains many Stretch Shrooms which live underground. Gold Rings also appear in this level, along with enemies like Fire Bros. and Koopa Troopas.
At the start of the level, the player must go down a red pipe leading underground. There is also a Hidden Block with a 1-Up Mushroom that can be seen at the far side before going underground. Once underground, the player encounters many Stretch Shrooms, a few Koopa Troopas, and two Fire Bros. throughout the section. Before the Checkpoint Flag, there is another Stretch Shroom that leads to the first Star Coin, which the player must duck to collect. After the Checkpoint Flag, there is a Red Ring with four stretching mushrooms where the player can collect an item. After this, there is a straight path with more Stretch Shrooms, after which is a yellow pipe that leads to the second Star Coin, Fire Bros., and a Gold Ring. If the player continues forward and goes to the far end when they pass through more Fire Bros. and a Gold Ring. The third Star Coin can be collected by going on the top platform with a red pipe that leads to the exit. If the player goes across the bottom, there are a few more Stretch Shrooms with lots of Coins until they reach the yellow pipe. This pipe also leads to the exit. The Goal Pole then appears with a Koopa Troopa along the steps. The player can only get to the top with Raccoon Mario. Furthermore, there are Hidden Blocks that can be created, with one of them containing a 1-Up Mushroom.
- Star Coin 1: This coin is on top of a Stretch Shroom, but is covered in Brick Blocks. The player must crouch on the right side of the Stretch Shroom to be taken to the coin.
- Star Coin 2: When the player sees the third Fire Bro., they must enter the yellow pipe to take them to a secret room with two Fire Bros. and the Star Coin.
- Star Coin 3: Before the exit, the player must run on the Brick Block ceiling instead of the lower Stretch Shrooms to find a hidden path to the third Star Coin. This references the Warp Zone from Super Mario Bros. and Super Mario Bros: The Lost Levels.