Pick up a Cannon Box from one of these ? Blocks right away; you’ll need one for retrieving Green Stars later in the level.
You can create bridges from these ? Blocks to explore the upper areas of this section, but there’s no pressing need to do so. You aren’t near a Green Star just yet. Be careful around the Madpoles infesting the waters here.
Explore this first Clear Pipe you find for a 1-Up. Another Clear Pipe below this one takes you farther into underwater caves. Rammerheads are swimming through the area, so be ready to move out of their way. Even the Cannon Box can’t stop them. Bloopers also make an appearance here.
Green Star #1
Here’s a Rock Block wall that must be blasted apart by the Cannon Box. Behind the wall is a Blooper and the first Green Star.
Green Star #2
When you reach these Spike Blocks, swim up toward the roof of the cave to find a side passage. This passage takes you to a room filled with Spike Blocks, Bloopers, and the second Green Star.
Green Star #3
Deep below the second Green Star is the main path you’re supposed to follow. You see an alcove blocked off by Rock Blocks, and behind them is a Green Star Ring. Collect the Green Coins that appear to earn the third Green Star. Use charged cannon shots on the wall near the Green Coins to pick up many at once without having to actually touch them.
Ignore the pipe you encounter shortly after picking up the third star. Instead, blast apart the Rock Blocks in the alcove next to it, and swim up the alcove to take a side route that will ultimately put you in better position to reach the top of the Goal Pole.