World 3-Tower (New Super Mario Bros. 2)

 is an autoscrolling underwater tower level in World 3 of New Super Mario Bros. 2. It is notable for the only level in the entire game to feature Spike Pillars. This level can be unlocked by completing either World 3-3 or World 3-A. This level has two exits - the first one unlocks World 3-4 and the second one unlocks and a Green Toad House. Mario has 500 seconds to complete the level.

Layout
Mario begins on a blue platform above the water with a single Fishbone. Two ? Blocks can first be found, with one of them containing a Fire Flower. After diving into the water, Mario will enter a green Warp Pipe on the right and upon reaching the following room, the level starts autoscrolling vertically. Two Fishbones can first be found, followed by brown moving walls, which will move after a set period of time. Some of these walls are spiked. More Fishbones will then appear. After the moving walls, Mario will approach Spike Pillars coming from both sides of the wall. Above the checkpoint enclosed in a safety zone, there is a ? Block containing a Fire Flower and a Brick Block that can be turned into a Gold Block. After passing by another Fishbone, the walls close an area with a Red Ring surrounded by four current-producing pipes. Seconds later, the top walls will open. More Fishbones and Spike Pillars will then appear, followed by a green pipe. Warping through will lead Mario to a small area with a ? Block containing a Fire Flower and the boss door. Here the player needs to defeat four Reznors on a single wheel with four rectangular ? Blocks to clear the level.

Star Coins

 * Star Coin 1: At the beginning of the level, there is a hole on the left side wall in the water. Instead of going through the Warp Pipe, Mario needs to swim into the hole and being careful not to swim too low. The Star Coin is above two ? Blocks above the water with a Fishbone. There are also three moving walls that cover coins.
 * Star Coin 2: In the main area, the player will navigate through several moving walls. The Star Coin is located above the second spiked wall on the right side of the area, guarded by a pair of Fishbones.
 * Star Coin 3: After the checkpoint, there is a Red Ring surrounded by four pipes. The upper left one is green, which is of different colors of the rest of the pipes. Entering it will take Mario to another room with the Star Coin. The player has to avoid the strong currents to reach it.

Secret exit
Mini Mario is required to access this secret exit. Located before the checkpoint and the first area with the Spike Pillars, there are two brown blocks which will move away to make way for Mario to pass through. Following the block on the right will bring Mario to a small pipe. After warping, the level will autoscroll upwards once again. This area has more moving walls, Fishbones and Spike Pillars. Along the way, there are several moving walls that close the area. Mario can collect coins in bubbles while avoiding them. When the walls open, Mario needs to swim to the top avoiding Spike Pillars. After the last two moving walls, Mario exits the water. Upon reaching the top, Mario can get two 1-Up Mushrooms in Brick Blocks if he's still Mini Mario. A red pipe will lead Mario to the tower's roof. There are two ? Blocks that have Super Mushrooms. After climbing the moving brown platforms, Mario reaches the Goal Pole.

This exit unlocks a Green Toad House and World 3-Warp Cannon.

Enemies

 * Fishbones (15)
 * Spike Pillars (20)
 * Reznors (boss) (4)