New Super Mario Bros./World 6-2

Within the mountain range, one can find a nice and sunny lagoon, complete with a sandy beach and palm trees. The geographical oddities of the nearby mountains cause the tide to significantly and regularly alter the water level. Beware of the many Spinies that inhabit this lagoon, as they've adapted to the constant tide changes with floating shells.

Level walkthrough
In the area you start off, you can observe one odd characteristic about Spinies. Whenever the tide rises high enough to submerge a Spiny, they will curl up in their shells to form a ball that floats on water, rendering them immobile. Their spiky shells are still a danger though. Enter the red pipe to the right. While the area before had minor tide changes, the water level here can rise and fall drastically. As Spinies will also be carried by the water, you have to be careful of Spiny shells coming from above, or rising from below if you're on a platform.

The second wooden platform after you come out of the red pipe gives you a good indication of how high the water rises. To the right of that platform is a palm tree. During high tide, try swimming just above this background feature to hit a hidden block containing a vine, which will rise into the sky. Climb the vine to the top, then jump on to the stone platform nearby. Jump to the next platform and hit the brick block to make a P-Switch pop out. Hit the P-Switch, then jump to the right using the flying question blocks. Follow the silver coins to the right until you reach the Star Coin on a temporary brick block platform.

Once you fall down, you can backtrack a bit to the right to reach a red ring. The red coins that spawn are mostly on the stone platforms above where the red ring was, just higher than the water level at high tide. To the right are several wooden platforms that demonstrate the danger of Spinies during tide changes. Try to stay in the water when the tide rises so that you're safe from their shells, and be especially careful when the water recedes. After the wooden platforms are two cannon pipes. The first pipe launches you into the air to a bonus area, leaving you on a moving platform. A line of flying blocks will approach in a wave, letting you hit them for coins and the occasional 1-Up Mushroom. Go into the yellow pipe at the end to skip a significant part of the level. You may wish to go left for the Star Coin.

If you're not concerned about getting coins and just want to save time, go inside the right cannon pipe to be launched over a tall stone pillar and into a wide tunnel. When the tide rises, swim up and right to reach the second Star Coin. Keep swimming right and get to the cannon pipe there. Enter it to be propelled out of the tunnel. Ascend up the stone steps to get to the yellow pipe, the one you'd use to exit from the bonus area. On the stone platform beside it, you will trigger the checkpoint.

Keep going to the right. You can drop down between two wooden platforms to reach a roulette block if you need a power-up. Drop down the next gap between wooden platforms. You should soon see another odd behavior of the Spiny shell. If the water level rises while they're below a stone ceiling, they will be stopped from rising any further by the ceiling. Eventually, you will come to a series of wooden platforms with many Spinies below. Some of the Spinies will get on this walkway when the water rises, while some will simply remain below if they're caught under the stone platforms.

Hit the lone block on the walkway to make a Star pop out. Grab it, and use it to defeat the many Spinies on and under the walkway. While invincible, be sure to collect the third Star Coin below the walkway, as it is much easier to do so if you don't have to fear the Spinies surrounding it. Keep going right until you get to a sandy beach. Two more Spinies remain until you get to the exit pipe. Go thorugh it, then hop up the wooden platforms to jump to the flagpole.

Star Coins

 * 1) Swim around the first palm tree after coming out the red pipe to hit a hidden block with a vine. Climb up the vine and jump to the floating stone platforms. Hit the lone block here to make a P-Switch pop out. Hit the P-Switch, then carefully jump on to each flying question mark block to the brick block platforms to the right. If you're fast enough, you can get the Star Coin on one of these platforms before they turn back into coins.
 * 2) Enter the tall cannon pipe with only one block attached to it to be launched into over a pit into an area with a low ceiling. Swim up during high tide to get the Star Coin.
 * 3) Below a walkway that consists of three wooden bridges, guarded by several Spinies. Getting a Star from the blocks nearby will make your job much easier.