New Super Mario Bros.: 8-2

It's an underwater level. There are water striders that will drop bombs on you, as well as make reaching the surface difficult. The ? Switches will raise the water level temporarily. There's a pipe at the top. It will take you to another room filled with water with striders and barrels. The ? Switch is on the left side. You'll be able to reach a mini pipe or a pipe overhead. The mini pipe leads to the first Star Coin. The regular pipe takes you to a room filled with brick blocks. Get the item in the item block if you need it, then pound the bricks. Stay towards the middle right to get the second Star Coin. There's a pipe in the water below. This area has a couple of striders and stack blocks. Use the ? Switch on the low ceiling to raise the water level and the stack blocks to block the striders off in one area. The right side at the top has the third Star Coin. The left side has a pipe to the flagpole.