You will find this star in the same general area as Swingin’ in the Breeze, so either take the carpet to the spinning platforms or directly Long Jump to the pole from the starting platform. Once you get to that area, head to the first seesaw and jump up to the next platform, where you might have to wait for the swinging platform. This will lead you to some donut blocks, which slowly fall after standing on them for a few seconds, as well as another seesaw. Upon reaching the upper donut blocks, keep an eye out for the flamethrower and continue past it, where you will have to wait on a moving platform.
Past this moving platform, there will be a wooden slope with some ledges, but you will want to continue beyond it. There will be two sets of donut blocks here, with a wooden sloped platform (with the slope being on both sides). Jump across the donut blocks, with one final flamethrower, and you will reach the area with a purple switch and the trickly triangles. The triangles start out with their point being up, but hitting the purple switch will flip them over, so the flat side is up. While the timer is active, you will need to quickly reach the top before they flip back over, causing you to slide off of them.
One quick tip is to try a Double Jump from the second triangle and onto the higher one. This will cause you to bypass a lot of the others and give you more than enough time to reach the top. Once you do reach the top, the star will be right there in the open.