Acorn Plains is the first world of New Super Mario Bros. U. The Acorn Tree resides here. Lemmy Koopa is the boss of this world, Boom Boom is a boss, and the Piranha Plant is the mid-boss.
- Before Acorn Plains Way: Bowser and his crew take over the Mushroom Kingdom and send Mario and his company flying all the way to the Acorn Tree.
- After Tilted Tunnel: Bowser starts a invasion on Peach's Castle.
- After Lemmy's Swingback Castle: Lemmy's airship is destroyed.