This is an automatically scrolling level with chain-link fences. You can only climb these as a cat, so you'll need the Super Bell. Get it from the first set of item blocks. Some of the fences move, so time your jumps. The first Green Star is in front of a vertically moving fence. Cling to the fence to get it. Ahead are two sets of two fences that open and close. Dive through the fences to reach solid ground at the end. Do not use the warp box yet. Wait for the level to scroll a little more and you'll see two more sets of fences. Behind them, on a cloud, is the second Green Star. There are a couple of ways to do this. You can jump to the right set of fences, then the left, then jump over the right fences, then repeat the process in reverse to return to solid ground. You can also try diving through the fences. Either method takes precise timing and may require several attempts.
Once you go through the warp box, you'll reach the midpoint, but the level keeps scrolling. Ahead are falling fences you must jump past. The stamp is just past the fences, high on the back fence. You can either climb the fence to get it or go through the pipe, pound through the cloud to get it, then go back through the pipe. At the top of the pipe is a cat gear. Spin it to make a platform appear under the third Green Star so you can reach it. Ahead are more clouds and some donut lifts, with horizontally moving fences. You'll have to dodge the fences and the Para-Biddybuds flying around. Once you reach the warp box, you'll warp to the flagpole. The cat gear will make a platform appear in front of the flagpole.
The stamp is of Cat Luigi.