Super Mario 64 on N64 - The Star Beyond the Rainbow

This course is in the same room as Course 15, at the complete opposite end in a similar hole. When you enter the clock room, go left and climb onto the platform to jump into the recess and dive into the hole from which a strange light escapes. It may be the hardest star in the game, notably because if you fall, you end up in the castle grounds and have to climb back up on foot before you can try again. However, if you're careful, if you take the time to grab a cap whenever you can, and if you don't take unnecessary risks, you shouldn't have any problems (especially if you follow this walkthrough). Start the course by taking the red coin right behind you.

Then take the cap from the starting cloud and do a triple jump toward the ring of coins to land on the first cloud. To take as little risk as possible, you can also head in the opposite direction and calmly go around so as not to arrive too fast. Take the coin and then fly down to the pink platform below. Like all pink platforms, this one has a cannon. Take the 3rd coin and talk to the pink Bob-omb to open the cannons. Since you're pretty much at the very bottom of the course, jump into the cannon after taking the 1-Up at the top of the green pole.

Aim all the way to the right to reach a fairly low cloud with a red coin on it. Then go back to the cannon platform and take the cap before jumping back in.

Aim at the sun and land on the other pink platform, then immediately jump into the cannon. Look for the cloud with green stalks hanging from it and aim above it (as soon as you can no longer see it inside the cannon's circle, you can fire). Land on that cloud to get the 5th and 6th coins. Take the cap again and fly toward the transparent cloud containing a red coin.

Take that coin and immediately turn back to reach the stalks hanging from the cloud you were on, to find the last coin. Let yourself drop from the stalk, take the cap and fly to the star that has appeared on a cloud not far from yours.