The Galaxy I was talking about is called, wait for it, Grandmaster Galaxy, which puts you to the ultimate test, it's one of the hardest Galaxies here, and you wanna know what Prankster Comet appears here? A Speedrun? Purple Coins? Etc.?
No, it's a Daredevil Comet, there are also no Checkpoints during this Comet, meaning that a simple screw up will send you right back at the start of the Galaxy, and to unlock the Comet, you need 9999 Starbits stored in the Toadbank, 241 Stars, and all 49 Comet Medals. (You need 240 Stars just to unlock the Galaxy itself.)
I wish you luck for those that are attempting to get this Star, you will need it, as it took me 10 tries just to get this Star. Make sure you stockpile lives just in case you fail a few times.
If you do manage to get the 242th Star, then congratulates, you just cleared Super Mario Galaxy 2 100%!