The sixth world is a dairy themed world. The many of the platforms are composed of milk bottles and metal plates, the swiss cheese that you encounter is merely eye candy that blocks your view of what lies behind it. Deadly enemies or helpful items may be found behind the cheese, so be sure to get a good look through the holes before you step behind it.
You will also quickly discover that the gooey ground in this world is not stable. You slowly drop through it like quicksand unless you jump constantly to stay above it. You can use the first hopping blue pig to rise above the ground and traverse over the giant bottles of milk, or sink into the ground and crawl below the bottles. Just be sure to continue jumping so that you don't fall through the bottom and die.
The first red metal plate that you encounter after jumping off from two columns will fall when you land so be prepared to jump off of it as soon as you land. As you continue, take the upper path beyond a very large block of cheese. Along the upper path, you can find a box with an invincibility bell inside behind the cheese. Collect it, and you can safely jump up and walk through the spikes on top of the next milk bottle. Then continue to run as far as you can while the invincibility still lasts.
Just beyond the metal plate with a red pig is another plate with an item box. This box contains a valuable heart that you should collect before proceeding to the boss fight at the end of the stage.
World 6-1 boss
Don't be fooled by the white clouds on the bottom of the screen, they are not solid, and Upa will die if he falls through them. You'll need to employ the flying blue dolls that pass through the area to make it from one column to the next. The item box at the very bottom of the screen contains a milk jar. While it's not hard to gather, you should only risk falling down to collect it if you don't have full health.
Boss: You probably expected the boss to be a large pink pig. You probably weren't counting on the platforms along the bottom of the screen to be so small and spaced apart. You have to decide whether it's worth trying to fight the boss by occupying the far left or right sides and pushing enemies into the pig from below, or whether it's better to make your way up to the pig's platform and deal with him from there. The pig's platform gives you a lot more space to maneuver, and the only thing you really have to worry about is jumping over the pig when he crosses from the opposite side to your side. Hit him three times with enemies, and you will defeat him. Just be careful when attempting to open the chest on the thin column.
This stage is very similar to World 1-2, where you had to dig through cake to reach the end, only in this case, you must dig through cheese. Patrolling the cheese are mice. There are two types of mice. The pink ones cannot chew through the cheese to make their own pathways. The green mice, however, are capable of chewing through the cheese, and will do so in an effort to get closer to Upa and bite him.
Although there are a few item boxes to find, there are also a number of other items hidden in the cheese. The first such item is hidden below the first item box. If you examine the cheese near the spikes, you'll find a heart. You can then walk through the spikes and sustain a unit of damage while you climb up to the item box, which contains a milk jar that restores all of your lost health. Just watch out for the green mouse that patrols the area.
A milk bottle can be found in the cheese to the right of the spikes. When you approach a row of giant milk bottles with two green mice patrolling the top and bottom pathways, dig the cheese to the left of the bottles to find an extra life. A hidden item exists along both paths. The bottom path hides a milk jar along the floor, but the upper path hides a heart just above the last giant milk bottle.
You will no doubt be lured into the region containing six item boxes in a row. Most of the contain apples, but one contains a heart, and another is empty. Before you approach the boxes, make sure that you clear away any mice that can harm you. Then gather the items, and climb back out to continue on your way.
On your way to the end of the stage, you must dig through a series of cheese with pink mice that occupy the small breaks in between, above and below. Stick to the very top or very bottom so that you don't release every mouse and have them chasing you to the end.
This short stage does not contain a boss. A treasure chest will drop down from the ceiling as soon as you reach the room with the blocks arranged in the word "NICE". Before you hit the chest, explore the upper portion of the letter E, and you should be able to find an extra life for your troubles.
The final stage of World 6 is a bit long, and very light on items that can help you, so you'll want to be extra careful and avoid taking damage as much as possible. From the start, hop along the ground to avoid falling through it and suffering a needless death. As you jump onto the short metal plates with red pigs on them, it's a good idea to rattle the pigs in mid-air so that they inflate and don't harm you when you land.
Be careful when crossing the rising platforms, as the spikes above them are quite dangerous. Wait until the first platform drops to the bottom, and hop on when it's on its way up. Then fall to the next platform and on your way through the small gap in the wall.
The next stretch is primarily filled with pigs. However, as you cross, be extra cautious of flying fish that zoom out of the ground below and fly in an arc. If you can't get out of the way quickly enough, use your rattle to inflate them before they hit you.
Towards the middle of the stage, the floor will be covered in jello molds. This can help you jump your way across the stage. In fact, they can help you reach the item box near the ceiling, which contains a heart. If you press jump while the jello mold is compressing, you will be launched into the air. The more compressed it is, the higher you will be launched. Use this technique to make it over the tall pillar at the beginning of the second half.
You will continue to be assaulted by flying fish appearing from the bottom of the screen as you cross the next set of pastry tube platforms. They will fly at you from both directions, so be sure to stop and turn around to rattle the fish that appear from behind you.
After crossing another section of floor covered by jello, you may or may not opt to jump up to the four metal plates near the ceiling. One lone plate lies between you and the next section of jello. As soon as you land on it, it will begin to drop. You must jump on to this plate as far to the right as you can, and jump off of it as soon as you land. If your timing is off, you won't reach the next jello.
Use the last two jellos to throw off the flying fish. Then hit the last item box to obtain a milk jar that restores your health. Then hop over the thin columns until you reach the boss.
World 6-3 boss
Boss: While the boss of this stage may be a large pig, this is definitely the hardest large pig you've ever faced. This one rides atop a cloud that floats back and forth near the ceiling. It will occasionally blink before sending two blasts of lightning down to the ground. To make matters worse, the entire floor is covered in jello, which will cause Upa to bounce throughout the fight. Another difference is that the boss doesn't spit out red dolls. Instead, he pauses and spits out little acorn-like creatures, but they behave the same as red dolls. Because of the near-constant motion of the boss, your best bet is to inflate the acorns and hit them so that they go up and down, or diagonally. Because of the boss' movement, you are more likely to hit the boss with the inflated enemies then if you try to push them horizontally. It takes five hits to knock the pig out. Then two treasure chests will fall to the ground before you proceed to the final world.
