New Super Mario Bros.: 1-A

We need 5 Star Coins to unlock this level, but it gives us an opportunity to save. It's an underwater level that is also an automatic sidescroller. There are sharks that will periodically appear and swim by, so don't swim around the right edge of the screen. Further along are yellow bouncy spheres that will push you around, making the area a little difficult to navigate. There's a P-Switch that will make lots of silver coins appear between the spheres. The first Star Coin is soon after, but some invisible blocks will make getting it a little difficult. There is a green pipe nearby that takes us to the second Star Coin. There is a Red Coin Ring before it. We get a much-needed Fire Flower from it, which we can use to take out the sharks. At the midpoint, we get a Starman from a random item block and take out some sharks. Next are some pipes creating currents that can push you into sharks if you're not careful. The third Star Coin is past a yellow pipe. It's near the ceiling. You can get it from the left side if you're small, or go around the right side. Soon after is the pipe to the flagpole. This opens up a path to the castle.