World 5-2 (New Super Mario Bros. Wii)
From the Super Mario Wiki
World 5-2 is the second level in World 5 in New Super Mario Bros. Wii. It starts off with a number of Wigglers. The player will then progress through a green Warp Pipe into an underground area filled with Big Wigglers, Swoops, and poison.
Before the underground section, the player has to progress in an area full of Wigglers. In the area is a POW Block found inside a wall, allowing the player to defeat most of the Wiggler. At the end of the area, a green Warp Pipe is found, which leads the player into the underground section. Once in the underground section of the level, the player sees another Star Coin floating above the poison, which requires bouncing on a Big Wiggler to get, and finds more Big Wigglers as they progress through the cave. After that, they have to cross a river of poison, which can be done by jumping on Big Wigglers in the area. If the player uses a Wiggler to bounce on the ceiling at at certain point, they reach a secret area with two Propeller Blocks necessary to get the last Star Coin, encased in the same room. They then reach the warp pipe leading to the exit. Next to the flagpole is another Big Wiggler which can be used to get on top of it and earn an extra life.