You start at the edge of a cloud. Run to the left and kill the Bird at the other end. Jump to the next cloud and kill the bird there. Keep going until you see a bunch of smaller clouds. Jump on those clouds and then jump again to kill the Bird flying above you. At the edge of the third one, you'll see a Witch flying toward you. Kill it and then carefully jump to the cloud below. Switch to your Spread Fireballs here so you can hit the Witches more easily. Continue to the right, avoiding the Witches and the eggs that they drop, until you see a huge structure. Keep jumping across the holes here and head up the stairs to the moving platforms.
Jump onto the closest one, wait until it reach the left side, and then jump to the next one. Wait for the next one to get to the top and just before it starts moving down again, jump to the one above it. You should easily make it. On this one, wait for it to reach the bottom and then jump to the Heart Container below. If you don't want it, just continue to the right and onto the roller coaster. Yay! It will start off slow but after the drop off it will speed up a lot. Various enemies will fly at you here so be on the lookout and charge up your special attack if you want. Once it levels off again there will be two Turtles in your way, kill them.
When it goes up again and back down there will another set of Turtles right at the spot where it goes down. Use your Spread Fireballs to hit them or you can just jump over them and then back onto the rollercoaster if you don't have time to hit them. Soon after that, two enemies will circle around you. The green one will blow wind at you, and the orange one will throw thunder at you. It's not too hard to kill either one but watch yourself here and jump over the wind and the thunder to avoid them. After awhile, they will disappear and then you'll take two loops and be finished with the rollercoaster. On the loops there will be two Birds coming from either direction at the top. Hit the one on the left on both and you'll be okay.
If not try to stay on the front part to avoid getting knocked off. At the end of the platform there will be a weird looking cloud below. These are like the platforms in the previous stage, except that they move in various directions. The first one will move to the left so you have to quickly jump to the next one. The remaining clouds will move in this order, left, down, and right. Stay on the last cloud and you'll be taken to a solid cloud. The next two will move down so quickly continue jumping. A Witch will usually appear here, so kill it and head right. There will be more Birds and Witches here but nothing really hard so I'll leave it to you. Just watch out for the Witches on the small clouds ahead. Climb the ladder to find the boss.
Boss: Mr. Chicken
Mr. Chicken has a beef with you... so now it's time to settle it. His attack pattern consists of flying around for a bit, tossing out an egg from directly below and two more to the left and right, and then diving at you. In order to avoid the eggs, either stay a fair distance away or a little to the left/right of him. Avoiding his dive is tougher. The best method is to just stay under him so that when he dives, he'll miss you completely. The other way is to stay as far away from him as possible, duck when he start his dive and he'll hopefully miss you. Hitting him is simple. Just use your Spread Fireballs. They hit multiple times and they will track him if some of them miss the first time. It'll take a couple dozen fireballs to turn Mr. Chicken into KFC.