This stage is Piranha Creeper Creek (4-2). This complete walkthrough will provide you with a 100% video playthrough and a screenshot of where you can find all the green stars. You should keep the Fire Ball Mario for the stage. The fireballs are the most effective ways to keep those snake Piranha Plants out of reach.
Game Play Walkthrough Video
Green Star 1
Jump onto the platform with the purple mystery box. You will then jump on top a string of Piranha Plants to get the Green Star. Princess Peach will be an easier character to pull the jumps, however Mario can succeed as well.
Green Star 2
There will be a pool of water where you can dive. Dive inside to grab the second star.
Green Star 3
A green star ring can be found near the end of the stage. Kill the Piranha Plants before you trigger the green star so that you will have an easy time to collect the green coins. You will obtain the green star once all the green coins are collected.
Before the green pipe to the third green star section, there is a secret area with some coins and the stamp. You will have to jump on the Piranha Head to access it. You can notice the hidden area by the little dent from the walls.