New Super Mario Bros./World 3-3

Along with Cheep Cheeps, Bloopers are a classic underwater enemy in the Mario series, having taken many lives due to their difficult to dodge movement patterns. Bloopers are so scarce in this game that they only appear in this level, and they're making their sole appearance count. Weave around these squids as you tactfully navigate pass strong water currents and the course's twists and turns.

Level walkthrough
As with any other underwater stage, you must enter by jumping into a warp pipe. Upon diving in, your first confrontation is against a lone Blooper, letting you observe the way it and its species move. If its not clear from this observation, Bloopers are more aggressive than Cheep Cheeps, and they will constantly chase after you. They move like a squid, shooting upward diagonally and slowly sinking down afterward. Like any other marine organism, you can take them out with a single fireball, so a Fire Flower is a valuable asset here.

Now, begin swimming to the right. You will start to encounter some Cheep Cheeps, as well as few Bloopers. As you go, look for a small sign pointing to the right. Swim up and right from where the sign is and you can possibly hit a hidden block containing a 1-Up. Eventually, the sea floor will disappear below, and some currents block your path forward. Descend into the gap below you to get to a small area with a pipe shooting out currents, a P-Switch, a Blooper and a Star Coin. The Star Coin is readily obtainable, but you must avoid or kill the Blooper to take it. Press the P-Switch to disable the water currents from the pipes, letting you go forward.

As you pass through the bottleneck with the currents temporarily disabled, you will trigger the checkpoint flag. Sink down pass the pipes. There is a Red Ring here, which spawns some red coins in a circle. Go right to reach a series of pipes, each higher than the one before. Go down the second one from the left to enter a bonus area. You've stumbled upon a Blooper nest, filled with coins and angry Bloopers. Move constantly, as the many Bloopers here can quickly overwhelm you. Especially dangerous are the Blooper Nannies, which can release Baby Bloopers around them after flashing rainbow. There is a roulette block in the middle of the room if you get hit. Your ultimate goal is to get to the bottom-right corner of this vast room, where you can get the second Star Coin. Swim to the top-right corner to find the exit pipe.

Back in the main stage, follow the currents of the pipe and go up, then right. There are some coins you can collect along the way, as you eventually get pushed to the a sign pointing to a pipe. You can take this pipe to exit the water, but you don't want to do that just yet. Let yourself sink down to the sea floor, and you can easily obtain the last Star Coin. As soon as you do, four Bloopers will materialize around you. Swim up immediately, altering your direction against the current coming out of the pipes. Go into the exit pipe to get to the surface. Jump on both pipes to the right, then jump to the flagpole to finish.

Star Coins

 * 1) Sink down upon reaching the first gap in the floor. A Star Coin is located here, guarded by a single Blooper.
 * 2) After the red ring is a series of pipes. Go through the second one from the left and swim to the bottom-right of the area you're sent to. The coin is there for you to collect if you can dodge the Bloopers in the way.
 * 3) Below the exit pipe pointed to by the sign, fall down the gap to get the Star Coin at the bottom. Start swimming up once you do, as some Bloopers will ambush you right after.