World 4-6 (New Super Mario Bros.)
From the Super Mario Wiki
In this level, Mario will ride another Dorrie, who is slightly larger than the one from World 4-1, to avoid toxic water. To get the first Star Coin, Mario should jump onto land, past the Red Ring. When on land, the player should keep up the pace with Dorrie. The second Star Coin is obtained by pressing a P-Switch, and then jumping to collect it. Soon, the player should see a ! Switch. Mario should wait for Dorrie's head to go up, and then he should jump and press the switch so he can go into a pipe that contains the final Star Coin. Soon, Mario should reach the Goal Pole.