Blue Coin #18
Near the beginning of the stage, you can hop on some ropes that are connected to platforms on top of poles. Get on these and when you cross over the wall, jump on top of it. Spray the mini-windmill blades on the one platform that’s not on the town side near the beginning to make this Blue Coin appear.
Blue Coin #19
From #18, you should see a tower of sorts nearby, which will have a Pianta standing on top of it. Get on top of this tower and clean the Pianta, then talk to him after to receive the Blue Coin.
Blue Coin #20
The next Blue Coin will be on top of the farthest tree from the others, which is the one closest to the water wheel. Spray some water at the center of the top of the tree to make the Blue Coin appear.
Blue Coin #21
From the previous coin, drop down and get on the rope that passes underneath the nearby bridge. Jump on the rope enough to bounce up and grab the underside of the bridge, where you will find this Blue Coin.
Blue Coin #22 and #23
There are two coins underwater, in the lake. The first one is within view of the cave in the far back, close to the one lily pad there. For the second coin, go to the other side of the landmass and search close to the wall, near one of the poles.
Blue Coin #24
On the lake side of the level, there are three stone/brick platforms sticking out of the wall not too far from the one Rocket Nozzle box. On two of these platforms are Pokeys and the one closest to the nozzle box will yield a Blue Coin upon defeating it.
Blue Coin #25
You will begin going up the main path leading to the huge windmill. Follow the path until you see a tall, grassy platform off to the side. Jump to this platform and spray water on it to make the Blue Coin appear.
Blue Coin #26
After procuring the previous coin, continue on the regular path until you reach the base where you can jump on the windmill blades. There, you will see another “M” shaped graffiti, so clean it to get the coin.
Blue Coin #27
Continuing from the previous coin, jump on any of the giant windmill blades and ride it to the top of the windmill. There, you should see a Pokey appear whenever you get to the top. Defeat this Pokey to get the Blue Coin.
Blue Coin #28
There are a number of platforms with ropes near the giant windmill, which is where you find all of the Red Coins. Find the highest one and get to it to find this Blue Coin.
Blue Coin #29
For this coin and the final one, you will need Yoshi, which requires you to unlock him in Delfino Plaza. When you do finally unlock Yoshi, you will find his egg right next to you at the beginning of the level. All of the fruits can be found underneath the cluster of trees, so bring the correct one back to have use of Yoshi. Once you have Yoshi, head to the town area and look for a blue butterfly around the one building by the female Pianta and the two kids. All you have to do, whenever you find it, is have Yoshi eat the butterfly to get the coin.
Blue Coin #30
There are two beehives on the cluster of trees just past the wall. Knocking them off the tree (jump on the hive) will cause a number of bees to chase after you. With Yoshi in hand, knock the beehives off the tree, then have him eat all of the bees. One of the hives will have a greater number of bees and when you eat the final one, the Blue Coin will appear.