Green Star #1 and #2
From where you start, walk forward toward the Thwomp, and slip into the alcove behind it to collect the first Green Star. The conveyor belts move fast enough that Captain Toad, in a full sprint, can only barely keep his place. To reach the second Green Star, you’ll need to walk around the whole level, avoiding Bill Blasters fired from Bill Blasters, to eventually reach a passage that was to the right of where the level began.
Inside this area is a Thwomp that you can use to ride up to the next section of the level, which is also where the second Green Star is located. Use a Thwomp to reach the next part of the tower.
Green Star #3
After the Thwomp delivers you to the this floor, you have to run across a conveyor belt that has two cannons firing Bullet Bills at you. Time your run to avoid getting hit, then make a quick left to reach the third Green Star.
Green Star #4 and #5
Now run across the conveyor belt and wait for the Thwomp carrying the fourth Green Star to rise up for you to collect it . Next, go into the tunnel nearby and get to the Thwomp that is rising up toward the highest floor of the level. Ride up and then wait for the Bullet Bill cannon to fire a shot, and follow the enemy until you fall into a small gap in the ground. You end up right next to the fifth Green Star.