World 4 (New Super Mario Bros. Wii)

World 4 is the fourth world in New Super Mario Bros. Wii. It features several tropical islands, therefore, most of its levels are water-themed and make rather good use of the Penguin Suit, which can glide over water and allow Mario to swim better. Also, on the map is a bridge guarded by a Porcupuffer that can jump up and make Mario and the gang endure an Enemy Course. This is also the first world to have a level on an Airship, like the ones in Super Mario Bros. 3. Wendy O. Koopa is the boss of this world.

World 4 also appears in Mario & Sonic at the London 2012 Olympic Games under the name "Cheep Cheep River" as the location of the Dream Rafting event. Porcupuffers, Thwomps, Cheep-Cheeps, and Bob-ombs appear in it, as well as the addition of Gooper Blooper. Also, Wendy (the boss of this level) appears as a costume for the player's Mii.

New Enemies

 * Mega Urchins
 * Porcupuffers
 * Huckit Crabs
 * Bloopers
 * Baby Bloopers
 * Blooper Nannies
 * Cheep-Chomps
 * Scaredy Rats
 * Climbing Koopas
 * Fishbones
 * Spike Pillars
 * Mecha Koopas
 * Rocket Engines
 * Boss: Wendy O. Koopa
 * Boss: Bowser Jr.