From the start, you’ll notice there are plenty of Goomba Towers around, so head right and take them out as you come across them. Slide down the ramp and clear the one Goomba Tower for a 1-Up Mushroom, should you need one. Atop the steps is a ?-Block with a Mega Mushroom. Use this to rush right, then leap up into the Stamp, before falling all the way down, through the grey bricks. Upon reaching the ground below, let the Mega Mushroom run out, then look for an invisible ?-Block on the left side that contains a Super Leaf. Move to the right, up the ramp, and stop at the wall of Blurkers.
There is Green Star #1 behind them, so do whatever you need to do to get there and grab the star. To the right of that will be the Checkpoint Flag, then some water you have to swim through. You do have to be mindful of the vents here, as there will be gusts of wind that come up periodically, which can knock you into the spiked blocks. After the second vent, you can get out of the water, where there will be a ?-Block that contains another Mega Mushroom. As soon as you grab it, hop back into the water and head all the way to the right. You should see a trampoline and some grey bricks above your head.
Perform a Ground Pound on the trampoline to get enough height to break through a second set of grey bricks, which are blocking you from collecting Green Star #2. Once the Mega Mushroom is gone, locate the green pipe to the right, but don’t enter it just yet. Instead, swim above it to uncover a hidden area from which the light is coming, where another pipe is located. This leads to a bonus room, with another Mega Mushroom and a P-Switch. Using the mushroom, collect all of the coins to get Green Star #3. Return to the main area, use the pipe and jump on the Goomba Tower to reach the top of the Goal Pole.