This stage is Hands-on-Hall (6-3). This complete walkthrough will provide you with a 100% video playthrough and a screenshot of where you can find all the green stars. The green stars and stamps in this stage are pretty tricky to find.
Game Play Walkthrough Video
Green Star 1
Open all the sliding doors that you come across. After getting the Goomba disguise, continue climbing the floors. You will open one that is empty. Walk inside the room and tap on the wall again, a hidden room opens with the green star. Watch out for the two Goomba enemies inside.
Green Star 2
At the part where you have to collect 5 keys. Head to bottom right to reveal some propeller boxes. Use the propeller box’s flying ability to collect the second green star in the middle. Keep your propeller box if possible to collect the stamp later on.
Green Star 3
When you reach the final corridor, you will find a orange mystery box. Avoid it and hit the tong in the back to reveal a purple mystery box. Enter it and defeat a Spike enemy to claim your final green star.
After the second green star, when you encounter the spikes that are tossing spikes into the camera’s view. You can exit the room and go outside. The stamp lies at the top of the platforms, keep on jumping up and reach the middle to grab it.