New Super Mario Bros./World 3-C

This level has many recognizable features of the southern beaches in World 3, such as blocks of stone platforms and crystal-clear water. As you cross the broken bridge to the castle, you will encounter the dreaded Spike Bass, who has returned from the oasis in World 2 to haunt this secret stage. Without the benefit of Spin Blocks, you will have many more close shaves with this monster fish as you attempt to traverse this course.

Level walkthrough
Once you head off the starting platform, surely enough, Spike Bass will begin its relentless assault. If you've played through World 2-A, you should be familiar with its method of attack. Once again, having a fire flower or a shell in your hands is helpful to knock out the giant menace temporarily. However, there are no Spin Blocks compared to World 2-A, so you will often be much closer to the Spike Bass' leaps. Make note of the elevation of the wooden platforms you jump on to determine whether you're safe from the bass.

Along this early stretch of the course, there are some red Koopa Troopas. Their shells are quite handy for defeating the Spike Bass, especially since you can use them to hit Spike Bass from a distance. Other than that, there are few notable things about this part of the level other than the thin wooden platforms. These unsupported platforms will fall into the water, so jump off of them quickly. Soon, you'll get to a bridge that consists of multiple falling platforms. You're safe from Spike Bass here, but you must use the falling platforms to drop to a Star Coin below. Quickly jump back out to evade Spike Bass.

After the long bridge, some more aquatic enemies will appear. Cheep Cheeps will jump out at you along with Spike Bass as you dash across the wooden platforms. Be quick but not rash if you want to clear this area unharmed. You will know the Cheep Cheep danger is largely over once you see some floating stone platforms. Jump along these stone formations to trigger the checkpoint flag. Keep going forward until you can see a Star Coin below a wooden platform. Unfortunately, you must jump into the dangerous water and quickly swim underneath the coin, then wall jump up the two stone platforms to collect the Star Coin. You can make this task easier if you manage to defeat Spike Bass beforehand.

A bit past the Star Coin is a P-Switch. Hitting it makes silver coins appear as well as turn coins into blocks. As soon as you hit it, quickly go right and hit the sole block to make a Star pop out. Grab it for the invincibility and follow the trail of silver coins as quick as you can. You will knock out some Paratroopas and jump over some falling platforms. If you're fast enough, you can get to a stretch of blocks below a red warp pipe you can go through. Otherwise, you'll just have to continue right to go into a green pipe instead. No matter which pipe you take, you'll end up at the flagpole area. The red pipe does toss you out on to a falling platform high above the water. Wait for it to fall to obtain the third Star Coin. Go right and go to the flagpole to end the course.

This is the last of the secret levels you need to clear for the shortcut to the castle. If you're interested in total completion or just curious, you can go back to World 3-Tower to experience the other levels you skipped.

Star Coins

 * 1) The coin is on a platform below a tall bridge. Stand on the falling platforms to drop down to it.
 * 2) You'll need to swim in the water for this one. While evading the Spike Bass, wall jump up the two stone platforms surrounding the coin to obtain it.
 * 3) After hitting the P-Switch, quickly follow the trail of coins to a red pipe. Jump into it and stay on the platform you emerge out on to drop to the coin.