World 1-2 is the second level of World 1 in the game New Super Mario Bros. 2. It is the first underground level in the game, and introduces red POW Blocks and the Mega Mushroom.
The level starts off with a green Warp Pipe. Above it is a green Koopa Troopa enclosed in Brick Blocks and the first red POW Block. Hitting the block destroys the Brick Blocks and overturns the Koopa. The POW Block itself turns into a Empty Block. Another POW Block is found to the left of the area, and reveals coins behind Brick Blocks when hit. Going down the pipe, the player automatically ground pounds and hits another red POW Block. The level is full of Koopa Troopas and red POW Blocks, which break empty Brick Blocks, trigger those containing items or reveal hidden items. Mario then comes across several Brick Blocks where there are three Koopas and two POW Blocks. A yellow Warp Pipe that Mario can enter soon follows. A Piranha Plant can be seen in the next yellow pipe. After the moving platforms, the player can see the first ! Pipe. To access it, the player needs to use a Koopa to activate a POW Block. Exhausting the pipe will release a Mega Mushroom. After several more Koopas and Piranhas, the player reaches the Checkpoint Flag. Mega Mario is needed to break several blocks to obtain another Star Coin between two sets of moving platforms. After that, a pipe leads back to the overworld, where another set of Brick Blocks can be found with a POW Block, followed by the Goal Pole.
- Star Coin 1: The first Star Coin is hidden in several Brick Blocks where the player can see three Koopas and two POW Blocks. To obtain it, the player has to activate the POW Blocks by using the red Koopa on top, revealing the Star Coin.
- Star Coin 2: The player needs to go down the first gold Warp Pipe they come across. The player then has to hit the P-Switch and dash to the Star Coin while avoiding the Koopas before the timer runs out.
- Star Coin 3: After the second Star Coin, the player will come across an ! Pipe. Mario/Luigi will need to spit fireballs into the pipe. Eventually, a Mega Mushroom will come out. The player should grab it and run to the right, because Mega Mario is required to break the blocks surrounding the Star Coin.