Proceed through the tube at the start of the level. You can claim a Fire Flower from one of the ? Blocks but you’ll want to keep a Cat Power-Up in standby if you grab this. 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 . Head through the pipe to reach a section with moving cloud platforms. Jump between them to claim Green Star #1 then ride the right platform all the way to the top and jump off. Dash across this upper tier until you reach a pipe, then take it to a green pipe that leads to a room with three Gold Koopa Shells . Kick them around for a ton of coins then head back to the cloud platforms. Snag the Green +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.
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. Another block along the way contains a Fire Flower – continue through the next pipe.
In this final section climb up the blocks to a ledge guarded by a Koopa Troopa. Defeat it then enter the pipe to be taken underneath this platform where the Stamp may be found. Claim it and return to the top, grabbing the Super Star from the block across the gap. Defeat the tower of Goombas to find Green Star #3 then continue to the exit.
For completing this world you’ll gain access to a Toad House which you’ll want to take advantage of.