The Double Cherry Power-Up is in front of where you start. This creates a clone of your chosen character, and you can have up to five clones running around. Some items and puzzles require that you keep a number of clones present, so try to keep your growing army under control and close together whenever possible. Typically they will stay synced up, but it is possible to separate them.
Green Star #1
The first Green Star is inside one of the crates to the right of a Clear Pipe leading up to a higher ledge. The other set of crates contains a Double Cherry, so nab it. With three characters running around, the havoc you can cause with a Fire Flower is impressive!
Green Star #2
Shortly after the first Green Star, you’ll find a pipe that takes you to a corridor guarded by a squad of Blocksteppers. Wipe them out, preferably from afar with fireballs, then use your Double Cherry clones to hit both Panels. This causes a Green Star to appear.
Watch yourself on the narrow paths here. Blocksteppers take up whole paths and when one goes down, they all go crazy and become hard to predict.
Stamp
Reaching the Stamp here is pretty simple. Stand on the ? Block directly underneath the Stamp, and use the ground pound. This will create a small tower of blocks that puts you within easy reach of the Stamp.
A lone Fire Bro guards the last part of the climb. He’ll try to use his jumping ability to stay away from you while throwing fireballs. You can surprise him by throwing your own fireballs into one of the Clear Pipes on the side of the mountain, which send your blasts up to the paths that the Fire Bro. might be standing on. Defeating him will cause a pipe to appear that leads to the final area.
Green Star #3
The final Green Star is in the Goal Pole area, and it requires you to stand on a Multi-Vator with at least four clones (or four players, if you’re playing multiplayer). This causes the platform to rise up to the star!