New Super Mario Bros./World 4-6

You have returned to the poison swamp for the last time, but this time the stretches of lethal water is longer than ever. No Scuttlebug, vine or paddling platform is enough to cross this vast body of deadly liquid, but Dorrie is back to help out. He's grown a bit since your last encounter but luckily not much faster. Still, try to keep up with this hardy plesiosaur, or you will be left behind without anywhere to go but into the swamp.

Level walkthrough
After some uneven terrain featuring Goombas and Koopas, you will find Dorrie parked at the edge of the swamp, waiting for you to begin the journey. Once you step foot on his back, he will start going forward, and there's no turning back. You will soon pass by your first island. You can choose to get on the island, which contains a power-up block, or duck as Dorrie swims underneath, netting you some coins. Soon, you'll pass a red ring and an island with the first Star Coin. Get on the island and simply walk up to the coin to get it. The red ring spawns one coin on the island and 7 in the gap below. Get the one on the ground, then throw a Koopa shell on to Dorrie's back and let it slide across the remaining red coins.

After the second island, you should see four coins arranged in an arc. They actually clue you in to the position of a hidden block, located at the center of the arc. Hit it to make a 1-Up pop out. Get on the island to the right of it, where there is a 10-coin block, letting you end up richer than if you just went under the island. The next island cannot be passed through from below. Once Dorrie dips his head into the water, be prepared to jump off. Carefully go past the three Piranha Plants inside the three pipes while trying to keep up with Dorrie. Once you clear this island, you will pass the checkpoint flag.

The next island you pass has a P-Switch on it, and to the right is a Star Coin surrounded by brick blocks. While it is optional, you can hit the P-Switch to make the Star Coin easier to get. Get back on to Dorrie as you start to pass through a tunnel. Pipes jut out of the ceiling, each with a Piranha Plant inside. The first two pipes contain a hidden block between them, which holds a rare Star! It can help you remain protected for the remainder of the ride.

You will soon see a red switch hanging from the ceiling. Leap up to the switch and activate it to generate two red blocks beside a pipe ahead. Get on to the blocks and go in the pipe to get taken to a secret area. Hop up the stairs here then slide down a slope, taking out several enemies in your path. The last Star Coin is located here, and it is not hard to reach. Before you go down the pipe to the right. Hit the block to make a 1-Up pop out. Exiting the bonus area leaves you ahead of the last portion of the Dorrie ride, skipping several Piranha Plants and Paratroopas. Go into the exit pipe to the right to get to the flagpole.

Star Coins

 * 1) The star coin is on the second island Dorrie passes, well within reach on land.
 * 2) The coin appears soon after the checkpoint, next to a P-Switch. Hit the P-Switch to turn the nearby blocks into coins, making it easier to collect the star coin.
 * 3) Hit the red switch on the ceiling as you pass by it, then hop to the pipe entrance with two red blocks beside it. Enter the bonus area and go right to collect it.