The sunny and wet World 3 has long coastlines and vibrant marine wildlife. The Cheep Cheeps here can grow to immense sizes, and some species are dangerously omnivorous. Be cautious when any Cheep Chomps are close by, or else you'll get swallowed whole!
The course starts above ground, but the bulk of the level takes place underwater. Go down the starting Warp Pipe to dive into the ocean. Immediately upon exiting the pipe you will see some Big Cheep Cheeps, which are often followed by small schools of normal-sized Cheep Cheeps. Despite their size, they're quite docile, so you just have to stay out of their path. For the first half of the level, Cheep Cheeps of varying sizes are all that you will encounter, and none of them pose much of a threat.
After some blocks, there is a Red Ring. Go through it and start sinking lower to collect the first three red coins. You'll have to swim up for the next two red coins, then sink back down and ascend diagonally for the last three coins. Be sure to avoid all of the Cheep Cheeps while you do so. After a short stretch of abyss and a wall surrounded by coins, you should reach the midway checkpoint. There is a roulette block past this checkpoint. Aim to get a Fire Flower if you don't already have it, since it will come in handy for the rest of the level.
After crossing a narrow gap between two walls, you will swim past the first current-producing pipe. Pipes of this type visibly spew out bubbles, which push you in the direction the pipe is facing. You will also come face-to-face with a Cheep Chomp, a deadly enemy that thankfully only dwells in this stage. This huge purple Cheep Cheep will lunge at you, mouth wide open. They can engulf you if you're not in Mega form, which will instantly kill you even if you're currently invincible. Like any aquatic creature, a well-aimed fireball is the best way to take them out.
Shortly after the Cheep Chomp appears, there is a Warp Pipe between two shorter, bubble-spewing pipes. Quickly maneuver yourself into the Warp Pipe while evading the Cheep Chomp's pounce. You will enter a smaller underwater area with a few Cheep Cheeps and tons of coins. More importantly, this is the location of the first Star Coin of the stage. Exit through the right Warp Pipe and continue swimming right.
The next Star Coin is out in the open, and should need no instruction to obtain. The two current-generating pipes around it are problematic, as is the presence of a nearby Cheep Chomp. The small nook the Star Coin is in means you are especially vulnerable to a Cheep Chomp attack, so it is advisable to only swim up to it once the Cheep Chomp lunges past you.
As you swim into a slightly more open area, you can see a P-Switch. Pressing it naturally turns nearby blocks into coins. Swim quickly to the right so that you can collect the final Star Coin that was previously surrounded by brick blocks. Of course, you can also skip the P-Switch and bump into the blocks to access it, but you can easily put yourself in the path of a Cheep Chomp, and the blocks might trap you when escaping if the gap you broke isn't large enough.
The Cheep Chomp remains a constant threat as you swim for the exit. The last stretch of the level is pretty straightforward. There will be another Red Ring between two square stone blocks. The red coins that spawn from it are positioned at the two stone blocks' corners. Although the red coin arrangement is simple, it is very difficult to get them all with the Cheep Chomp right behind you, since you have to move around in a relatively small area. Just to the right of these two blocks is the exit Warp Pipe. Enter it to arrive at the flagpole.
- Around where the Cheep Chomp first appears, there is a green Warp Pipe sandwiched between a red and a green pipe that spews produces currents. Go through the Warp Pipe to enter a small area with the Star Coin.
- This coin is plainly visible between two water-spewing pipes, but the Cheep Chomp nearby may pose a danger.
- The coin is surrounded by blocks a bit past the P-Switch. Hitting the P-Switch is the safest way to obtain it.