Green Star 1: It is floating in midair on the third bridge. Stomp on the Hop-Chop on the stairs and place it below the Star. Jump on the spring to collect the Star. Watch out for the searchlight.
Green Star 2: On the third bridge, there is a cracked wall. Let the searchlight detect you, and lure the Cat Bullet Bills toward it. Beyond this wall is a Mystery Box. Inside the Mystery Box, there is a series of grey brick stairs and a searchlight covering over half of the screen. Quickly climb the stairs, dodge the Cat Bullet Bills and collect the Green Star.
Green Star 3: At the stairs, there are grey and black bricks surrounding the third and final Green Star. Let the searchlight detect you and lure the Cat Bullet Bills toward the bricks. Once the bricks are destroyed, collect the Star.
On the third floor past the checkpoint, the Stamp is floating right above a group of bricks and Question Blocks. However, a searchlight is there to prevent you from collecting it. When the searchlight moves away from it, quickly jump on the blocks and jump again to grab the Stamp.