Tilted Tunnel

Tilted Tunnel, or Acorn Plains-2, is the second course of Acorn Plains in New Super Mario Bros. U. It is an underground course with slanted pipes and shifting crystals. It is the first course to feature the Fire Flower and to have a Secret Exit. After this level is completed, a cutscene will show the flags on Peach's Castle being replaced by Bowser's flags.

Layout
The course is filled with slanted pipes, which Piranha Plants come out of, and shifting crystals, which move when the player gets to a specific point. Later in the course, there is a long pathway where the player can slide into Goombas to gain 1-Ups. There is also a bonus area full of Buzzy Beetles and a POW Block. The player can toss the POW Block to make a shower of coins fall down.

Star Coins

 * Star Coin 1: At the end of a long slide with Goombas.
 * Star Coin 2: At the end of a corridor full of slanted pipes, the player must use a Koopa Shell to hit a Brick Block. The Brick Block contains a vine that leads to a sub-area, in which the player can use the Cannon Pipe to get the second Star Coin.
 * Star Coin 3: Once the player runs into two blue crystals, one with an Arrow Sign on it, the player must Ground Pound the latter crystal to reveal the path to the Warp Pipe, which leads to the sub-area with the final Star Coin in it.

Secret Exit
Near the end of the course, there is a pink crystal with a Red Ring that will shift upwards. The player can use that crystal to jump up across the ceiling on top of the course. The player can then jump off a blue crystal to reach an even higher ledge. Now Mario has to run all the way across the last part of the cave section. There is a hidden Warp Pipe at the back. Getting to this secret exit unlocks Blooper's Secret Lair.

Enemies

 * Koopa Troopas
 * Goombas
 * Piranha Plants
 * Buzzy Beetles