The level starts off with you in front of a green pipe, with a Koopa Troopa roaming in front of it. Ignore it and enter the pipe to begin the actual stage. You can claim a Fire Flower from one of the ? Blocks at the beginning, but you’ll want to keep a Cat Power-Up in standby if you grab this, as it can be useful later. Break the purple blocks to reach a hidden area where you’ll want to defeat the Koopa Troopa then toss it’s shell around to quickly collect all the coins. Continue heading right and defeat another Koopa Troopa, but try to keep it’s shell in tact if you are hunting for a secret.
As you move towards the end of this segment hit the blocks along the back wall. There are actually three in a row going straight up, the top one is a 1-Up Mushroom (it’s hidden). Head through the pipe to reach a section with moving cloud platforms. Jump between them to claim Green Star #1, but there is another secret here. Above the right set of cloud platforms, there is a hidden upper ledge that will eventually lead to a golden pipe. There will be three Gold Koopa Shells in here, so get them moving to earn a bunch of coins.
Exit to the main level and return to the cloud platforms. Snag the clock on the mid level then go through the tube to reach the checkpoint. The back wall has a second level of blocks that yields a Fire Flower if you need it; both are invisible, but you can use a Ground Pound to uncover their locations for a quick second. Climb up the blocks to the right and jump into the Mystery Box . Defeat the two Koopa Troopas in time to claim Green Star #2 then exit. The crate to the right of the Mystery Box will contain some Mini-Goombas, so be mindful of breaking it.
The one block along the bottom contains a Fire Flower – continue through the next pipe. There are two hidden ?-blocks above the first one in this new area, allowing you access to a clear pipe in the wall. Take this pipe to a hidden area below you, which houses the level’s Stamp.
Return to the top, grabbing the Super Star from the invisible block across the gap. Defeat the tower of Goombas to find Green Star #3 then continue to the green pipe. This leads to the exit, where you will find the flagpole.