The harsh desert of Sand Canyon is a hostile environment to be in, with deep mounds of sand that slows travelers down to a crawl. Slow movement isn't the only nuisance caused by the dust whipped up by the winds that shape the sand dunes, as the bearer of this level's Heart Star can attest to. She needs help cleaning up an old building in the middle of the desert, and you'll need a certain ability to help her out.
The arid desert naturally contains a lot of sand. In fact, certain parts of the ground is entirely covered by it. Like you've briefly observed back in level 2-6, the sand will slow you down, so be cautious of enemies when running across it. You can also choose to simply fly over the sandy ground, but there is another danger that restricts you from doing so. There are several cacti growing in the desert sands, and enemies called Boten reside at the top. Whenever you get close, the Boten will extend its spikes and drop down to try to harm you. You can swallow Boten for the Needle ability. There are also shovellers called Doka that digs up mounds of dirt and fling them at you.
Besides these two new enemies, there are also some Keke flying around on their brooms as well as Bobo simply roaming about. Be sure to grab the Clean ability from the Keke if you want the Heart Star, and try to keep it until you reach the section where the ability comes into play. Eventually, there will be slopes that contain shifting sand. The sand will affect your movement, so be careful of the loss of speed if you're going uphill on one of these sand pits. Toward the latter half of the section, there is a door that leads to an area that lets you choose between Coo and Chuchu. It doesn't matter who you choose, as you can still go for the Heart Star as long as you have the Clean ability.
Rock and sand
The enemies here are certainly more varied than in the area before, with Waddle Dees, Como, Sasuke and Sparkies all roaming about. The main threat here are the Como, which hang from the ceiling of rocks, some of which are quite low to the ground. While it makes them easier to hit, they are also much harder to evade. There are more patches of sand that slow your movement, but the majority of them can be cleared in a single jump.
Soon, you will come across a single door in the middle of the section. Going through the door lets you get some stars, but there also appears to be two doors leading to an isolated chamber from the area you're in. Back in the main level, you can actually go into the stone blocks hanging down either side of the visible door to reach a hidden door. The door leads to the aforementioned isolated area, where you can get a great combination of two Health Drinks and one 1-Up. Past the secret doors, there is nothing noteworthy except for some enemies trapped in Star Block pyramids. You can easily ignore them unless you want the abilities they grant.
Heart Star: Dusting the ancient ruins
There is a bunch of Bukiset lined up one after the other, including one that gives you the Clean ability in case you have yet to obtain the power or have lost it before reaching here. Before you enter the door of the large structure, be sure to climb up to its roof to find some extra stars. After that, enter the building to find the bearer of the Heart Star, an overworked janitor cleaning up the ruins. If you have the Clean ability, you can help her by going into other rooms in the structure, then using your ability to get rid of the grey dust. You do have to watch out for Nidoo pretending to be a door in the first room, then a Mariel crawling toward you in the second. Once out of the building, you can feel free to ditch your Clean ability to get a different one from the Bukiset. Just like the left side of the structure, you can jump up to the roof to collect some extra stars.
Shifting sand tunnels
Every surface in this tight area is made of sand, and every slope contains sand that is moving downhill. This makes it difficult to navigate your way around the winding tunnels, as the sand will slow your movement, and the narrow tunnels make it hard to just jump up the slopes. Fortunately, there are few enemies in this section, mostly consisting of black blobs that can't damage you as well as the occasional Propeller.
The entire stretch of this section is just a wide, sandy plain, punctuated by small pools of water. The sand makes progress really slow, so try flying or hopping across the sand instead to get cross this area faster. The water is mostly empty, but the larger ones often contain Squishies, while one even contains a Maxim Tomato. Outside of the water, Pterans frequently swoop down at you from the sky, while the occasional Yaban can fire at you from high ground. There are also Wapods that emerge from pots in the ground, but they are easily defeated by attacking the pot. The exit door is right at the end of this straightforward section.