Acorn Plains

Acorn Plains is the grassy world of New Super Mario Bros. U. It lies south of Layer Cake Desert, west to Sparkling Waters and Soda Jungle, and south-west of Frosted Glacier. It is a plains world with acorn trees, shrubs, jagged mountains reminiscent of some of the backgrounds in Super Mario World and the world's most defining feature, the Acorn Tree. This special tree is one of main sources of the game's new power-up, the Super Acorn. It can be found in the game's intro, Acorn Plains' map, and said world's first level. The name is derived from acorns, a nut, which are known to be eaten by squirrels and can grow into trees. This world has at least seven levels, two of which are the Fortress and Castle levels, a red and green Toad House, a Piranha Plant Enemy Course, and a spot where a magenta Baby Yoshi walks near. The Castle boss of this world is Lemmy Koopa.

Levels

 * Acorn Plains Way: The first level of Acorn Plains. A simple grassy level that introduces the flying squirrel enemies, Goombas, Koopa Troopas and Piranha Plants. The Acorn Tree, slanted mountains, and Princess Peach's Castle can be seen in the background. It also introduces the Super Acorn.
 * Tilted Tunnel: The second level of Acorn Plains, it is an underground level with tilted pipes and moving crystals.
 * Crushing Cogs Tower: The tower level of Acorn Plains.
 * Yoshi Hill: The third level of Acorn Plains, it introduces Green Yoshi and Monty Moles.
 * Mushroom Heights: The fourth level of Acorn Plains. It is an athletic level and it introduces Balloon Baby Yoshi.
 * Rise of the Piranha Plants: The fifth level of Acorn Plains. It is filled with slanted grounds and Super Piranha Plants.
 * Lemmy's Swingback Castle: The Castle level of Acorn Plains. It is filled with lava and moving platforms held by chains.

Challenge Mode original courses

 * The Goombrat Stomp
 * An Acorn Plains course, presumably Rise of the Piranha Plants.

Boost Rush Courses

 * Acorn Plains Way – Easy Pack
 * Mushroom Heights – Acrobat Pack
 * Lemmy's Swingback Castle – Flying Squirrel Pack

Trivia

 * In early builds of New Super Mario Bros. U, the Acorn Plains map looks substantially different. The map was significantly less detailed, the Acorn Trees did not show the Super Acorns, the map had two red Toad Houses, and the green Toad House was in a different spot, there are two Enemy Courses instead of one, and the spot where the Balloon Baby Yoshi was, is gone.
 * Previous footage of final Acorn Plains map have depicted the pipe that the Piranha Plant is nesting in as green, instead of red.