Cloudy Park is a difficult area to access, since it is high up in the sky. However, there is a very tall mountain that reaches into the clouds, making it a gateway to the rest of the park. Climbing up the mountain will not be an easy task, as the mountain's inhabitants and loose boulders will obstruct you. At the top of the mountain are flowers dirtied by dust. You'll need a feather duster to clean them up, and while a broom wouldn't do the trick, perhaps using it with a feathered-friend will...
Climb into the clouds
The starting area is very simple, and you just need to run down the path while avoiding or defeating the enemies. Be sure to grab the Clean ability by swallowing Keke's broom, as it will become useful for later. You will past through a brief transition area with Rick available as a partner, then on to another uphill path with many Togezo, Yaban and Scarfies. The Scarfy is a new enemy with a harmless appearance, but trying to inhale it turns it into a terrifying aggressive monster, so defeat it with an attack instead. Past another brief transition section, this time with Nago, you will continue your climb, fighting off Sir Kibble, Gabon and Gordos. Through the door at the end of this section, Pitch is available if you want it as your partner.
Boulders up above
You will continue yet again on the uphill path. There are a number of Galbos napping on the slopes, and soon a Health Drink will appear if you wish to heal off any lost health. Watch out as you approach it, as the screen will start auto-scrolling to the right, and you better drop down and run through the lower tunnel to avoid getting crushed. You will also pass underneath some boulders, which will dislodge and tumble after you. Stay ahead of the boulders while defeating any enemies that block your path until you reach the door. The screen stops scrolling here, and you get to see another mysterious Batamon, narrowly avoiding a boulder in a visible but inaccessible part of the level. At the end, you can choose to take Chuchu along with you.
There are plenty of Shotzos littering the various levels of the valley in this section with cannonballs, so navigate around this place with care. There are plenty of stars you can collect, but also Sir Kibble and Mariels that you need to be careful of. As you drop down to the bottom of the valley, there are two different paths you can take, both of which lead to great rewards. The left path lets you get a 1-Up dangerously close to a Shotzo, while the right path contains an Invincibility Candy! Be sure you grab the candy so that you're completely safe as you make your way up the right side of the valley. Check the various nook and crannies as you do, as one of them contains a helpful Maxim Tomato. Through the door, you can now choose from either Kine or Coo to be your Animal Friend. Coo is the one you want to pick, for both getting the Heart Star and for its general usefulness.
More rolling boulders
There are plenty of boulders lodged in the ceiling as you go left in this area. Unlike previous boulders, these easily dislodge and will roll right at you. There is usually not much space to evade them and it is useless to outrun them, so look for any pits covered by thin platforms that you can duck into whenever a boulder gets near. If you can fly or hover, you can also evade boulders by hovering in place of a previous boulder's spot. The tunnels will soon widen, but now you must dodge boulders with a well-timed jump instead of staying in a single position, although hovering along the ceiling still lets you dodge them effectively. The tunnel will become narrower once again, and you must duck out of the path of some more boulders before reaching the door.
Heart Star: Dusting some dirty flowers
The concentration of enemies in this final section is much lower than before, but there are a lot more bottomless pits around, so avoid falling in. There are some Keke here in case you've lost your Clean ability on your way here. Like the first levels of every previous world, there are flowers here that will reward you with a Heart Star if you help them out. The flowers here are dirty due to the dust that gets swept around on the mountain, and you must use Coo and the Clean ability to clean them. Simply approach them and use your attack to feather dust them. The clouds floating by the foreground will obstruct your view, so be sure not to trample a flower as you fly through the section. Also note that Coo will stop hovering if you use your attack, so be careful when dusting a flower near a pit. Once you finish dusting the flowers, a sound will play indicating that you've earned the Heart Star. Go through the exit door at the end of the area to claim it.