The first obstacle you come across in this level is a sliding door that will only move if you tap it with the touch screen. Expect to see many of these doors throughout the level. Additionally, there are large gongs you can tap to find extra items or Coins.
The steps here collapse into a ramp, while a Spike tosses spiked rollers down the ramp to try to crush you.
Behind these sliding doors is a pair of P Switches. The one on the left lowers the stairs up to the next floor. The one on the right opens up a hidden door to let out a pair of Goombas. They drop Goomba Masks that you can use to fool enemies.
Green Star #1
On the third floor, you come across a set of double sliding doors that, when moved, appear to hide nothing. Approach the wall behind them and tap it to reveal a hidden room with two Galoombas, a pile of Coins, and the first Green Star.
As soon as you reach the rooftops of the level, you can see the second Green Star in a pit directly in front of you.
You need to find five Key Coins scattered throughout the area to reach the Goal Pole. The first is next to a pair of Thwomps near the start of this section.
Green Star #2
Reaching this Green Star requires you to first grab a Propeller Box, then you must jump into the pit, grab the star, and use the Propeller Box to escape certain doom.
Two more Key Coins are found on the ledges above the first Key Coin, and the last two can be found not too far from these (8). Getting the last two unlocks the Warp Box to get back inside the castle. Be on the lookout for Goombas and Spikes during the last stretch.
Stamp
You might notice that the Spikes throwing spiked rollers toward the camera aren’t hitting any walls. They are actually tossing the spiked rollers through large exits that lead back to the outside of the level, where you can locate the Stamp. The Cat Power-Up or a Propeller Box is essential for reaching this item.
Green Star #3
The last Green Star is found in a Mystery Box that appears only after you ring the gong at the end of the last corridor. You have to ignore the Warp Box that you see at first, as the gong is farther down the corridor. You’re warped to a small room with a Spike. Defeat him for the Green Star.