Mini-Mega Island (or World B) is the second secret world in Newer Super Mario Bros. Wii. It is unlocked by completing the secret exit in Pillar Pass in Rubble Ruins. Completing the fortress will unlock a shortcut to Bubble Basin in Mushroom Peaks.
Mini-Mega Island takes place on a grassy island mostly based on World 1 from New Super Mario Bros. Wii. It has a "big and small" theme, featuring larger versions of several enemies, such as Mega Goomba, Mega Urchin, and more. Much of this world is based on World 1 from New Super Mario Bros. Wii.
|Level number||Level name||Preview||Description|
|B-1||Mighty Meadow||This forest themed level introduces giant versions of enemies, such as the Mega Goomba.|
|B-2||Pintsized Plains||A plains-themed level featuring small areas within the level. This level features an underwater portion which introduces the Mega Urchin.|
|B-3||Troopashell Track||This level takes place in a valley filled with giant Koopa Troopa shells. It also introduces the Mega Stalking Piranha Plant.|
|B-4||Cheepcheep Creek||An underwater level featuring giant underwater enemies.|
|B-Fortress||Formidable Fortress||The first half of the level takes place in a fortress with Thwomps and Skewers. The pipe after the checkpoint takes you to an area outside in a plains with many big enemies. There is no boss in this level like all other fortresses in the secret worlds.|
- The Minimega Music House is the official Music House for World B. It can be accessed through completing B-2.
- The music in the normal levels are a remix of the theme for World 1 from New Super Mario Bros. Wii. In addition, most of this world is based on World 1.
- This world's name is related to Super Mario 64's Tiny-Huge Island.