This is an underwater level. In underwater levels, you can not jump on enemies to defeat them. Practice swimming in the nearby pool if necessary, and then go down the yellow pipe to begin the level.
The level starts off with rings of coins and swimming cheep-cheeps, swimming in loops. When you see a ? block, jump up into it to get a Fireflower. Now you can blast away at the fish in your path. Just to the right, you'll see the first star coin guarded by a spiny cheep-cheep. Dispose of the spiny fish using the fireflower and then carefully swim down to grab the coin.
Next, you'll see a roulette block that can grant up to 50 coins. Get as many as you can, but beware the giant cheep-cheep that passes through. Soon, you'll see a yellow pipe and a ring of cheep-cheeps surrounding some coins. Go around them and get in the yellow pipe. At the bottom of the new area, you'll see a star coin in a downward flow. Grab the star coin, but be sure to swim back up as quickly as possible to avoid being sucked in. Once you're done, exit via the green pipe.
You should be at the midpoint flag by now. Hit the first ? block you see to the right to get another fireflower. Navigate through the rings of enemies ahead until after you see a green pipe. On the first hole in the ceiling after seeing the pipe, swim up into it. You'll find the third and final star coin.
After this, there are just a few more enemies to swim past, plus a P switch that creates a bunch of coins. Beware though; one of these fish are giant, and can eat Mario in a single bite! When you reach the end of the cave, go up the green pipe. Run and triple jump up the platforms to get an extra life on the flagpole.
Ways to Lose[edit]
Without a fireflower, it can be easy to be caught defenseless. Water levels often leave the player without a method of self-defense. Try swimming carefully to avoid enemies.