World 6-5 (New Super Mario Bros. Wii)
From the Super Mario Wiki
The level begins with a Porcupuffer chasing Mario throughout the level. The first Star Coin can easily be obtained by getting on a ? Block or swimming to get it. Then the water starts frequently rising and draining. After the midway point, the Mario can get the second Star Coin which is on a low platform. Next, there will be four ? Blocks. If Mario jumps in between the second and third ones, a Hidden Block with a Beanstalk appears, giving access to the third Star Coin and the secret exit. After the Beanstalk, Mario must enter a Warp Pipe to the flagpole finishing the level.