|World 4 (New Super Mario Bros.)|
|Game||New Super Mario Bros.|
|# of levels||10|
World 4 is a unlockable thick forest world with toxic water seeping through the ground in New Super Mario Bros. It is a bonus world that is only unlockable if the boss of World 2 is defeated while Mario or Luigi is in Mini Mario mode. Defeating the boss of this world allows Mario to progress to the snowy World 5. The world is largely inhabited by Koopa Troopas and Goombas, with Scuttlebugs dropping down from the boughs of the trees. As aforementioned a large swamp of toxic purple water flows through the world. If Mario or Luigi were to touch the water, they would die instantly. The boss of World 4 is Mega Goomba that can only be defeated by using elevators to reach its head.