Rainbow Ride is definitely a dangerous course, as one slip-up usually means you are dealing with a lost life. It is also the course that has some of the longest stars in the game, simply because of the flying carpet rides you can’t really skip (for the most part). When you begin, you will be put on a platform that has one of those flying carpets right in front of you. This will follow a predetermined path, with some obstacles you will have to jump over along the way. There will be a flamethrower that you can trigger a little earlier by jumping on the platform with the Amp.
Note that on the starting platform, you can Long Jump to the one pole you see a little bit in the distance, which will allow you to bypass the first carpet ride. Anyway, after the carpet ride, you will be right before four spinning platforms, with a Lakitu tossing Spinies down at you. You will find three ways to go here, but the one you’re looking for is another flying carpet. This one will take you through more obstacles, but end with a choice of another two flying carpets. If the carpet is coming towards the camera, you will want to take the one on the right.
At the start of this final carpet ride, you will have to contend with a large spinning platform that is shooting some flames from the bottom tip of it. This platform also has some “arms” sticking off of it, meaning you will have to jump over them multiple times as the carpet circles it. Once you are finally free from that spinning platform, there will be a few more obstacles before you will have to jump off and onto some donut blocks. You will be right there at a flying ship, which is where the star is located. It will be right there, in plain sight, on the ship.