This stage is Boiling Blue Bully Bell (Castle-4). This complete walkthrough will provide you with a 100% video playthrough and a screenshot of where you can find all the green stars.
Game Play Walkthrough Video
Green Star 1
Gather all the green coins after activating the green star ring.
Green Star 2
Enter the purple mystery box where you can see when you collect the stamp. Push the Bully into the lava to win the second green star.
Green Star 3
You will see a green glow when you get to a rolling platform with the rotating pikes. Tread carefully to collect the green star.
The stamp is found at the left side of the stage on path with the arrow platforms.