This is an automatically scrolling level. Climb up the platforms on the back wall and you'll see something move from the lower right corner. It's a mass of Fuzzies that will follow you around. Touch the mass is instant death. Grab a Tanooki Suit and go past the Para Dry Bones. Go up the tilting platform and you'll find the stamp in an alcove behind a crushing wall. As you climb higher, you'll find more moving walls. You'll find the first Green Star on the right side, under a cloud. Ground pound the cloud to drop through it to get it. Go up and to the right, where you'll find a POW Block. You'll find the second Green Star over a tilting platform. Ahead is a series of moving walls that will close one by one. Use the springboard to reach the walls and jump up to the third Green Star. Above it is a cloud and a door to the flag.
The stamp is of a Fuzzy.