World Mushroom-A

 is the first secret level of World Mushroom in New Super Mario Bros. 2. This is an ice-themed level taking place underground. Common enemies here are Dry Bones and Spiked Balls.

Completing this level unlocks World Mushroom-3, skipping World Mushroom-2 and World Mushroom-Ghost House.

Layout
Mario begins at the bottom of the deep ice shaft and must make his way upwards to the surface. Ice blocks are common here and acts as platforms. A ? Block can be seen at the right which releases a Fire Flower. Moving upwards there is a spiked ball moving around the floor where several ? Blocks ad Brick Blocks can be found. The Brick Block on the left contains many coins and can be turned into a Gold Block when hit a set number of times. Next, a spiked ball will then drop from above, destroying several Brick Blocks. On the next few levels, spiked balls will continuously roll from the left or right side of the screen. At the top of these areas is the checkpoint. Several Dry Bones appear, followed by a Red Ring. The next area has two fast moving spiked balls bouncing away from walls and each other. On the next level a large spiked ball will begin crashing down and destroying Brick Blocks on its path. Another spike ball will then roll down, followed by the exit pipe. Back in the overworld, there are several ice blocks present, which helps Mario reach the top of the flagpole a short distance away.

Star Coins

 * Star Coin 1: The Star Coin can be seen early in the level but it is tricky to obtain without taking damage. The player needs to slide through the narrow gap of the wall enclosing the Star Coin while avoiding the moving spiked ball at the same time.
 * Star Coin 2: Just before the checkpoint. On the second set of continuous moving spiked balls, there is a fork on the path. The player needs to take the path on the right to obtain the Star Coin.
 * Star Coin 3: When the player meets the two fast moving spike balls, the player needs to make his way to a ice block on the other side of the area, where a Dry Bones is. The player then needs to activate the ? Switch above him and wait for the larger spiked ball to destroy the two smaller ones. With accurate timing, the player then needs to make his way down and obtain the Star Coin.

Enemies

 * Dry Bones
 * Spiked Balls
 * Giant Spiked Balls