This stage is Plessie’s Plunging Falls (1-4). This complete walkthrough will provide you with a 100% video playthrough and a screenshot of where you can find all the green stars. We will also note a secret 1 UP.
Game Play Walkthrough Video
It should be noted that this stage is played twice to obtain both the second green star and the stamp.
Green Star 1
It’s right on top of the second group of enemies. Use the speed ramp to jump higher and collect the first green star.
Green Star 2
Green Star 3
The third green star is available near the end of the stage. When you see the last star, hit jump after you pass the speed ramps, and you will be in the clear to obtain the last green star.
After getting the secret 1UP, head for the right path instead of behind the water fall. You will have to be careful not to fall into the edge of the water. You will then obtain the stamp for the stage.
Other Notable Secrets
This is not much of a secret. However, at the path where you can jump up the levels. Pick the left one to hop onto enemies. You will find a secret 1UP at the top of the level.