you have to get every star, green star, prankster comet and comet medal
use a comet
cuz i diii
in the first super Mario galaxy you need to get close to finishing the game or just beat that area ( Terrace, Fountain, etc.) Lets take the Good Egg Galaxy for example, u have got to get all the stars available so far in that galaxy, later you will get an alert saying that a comet has just appeared there in the second Super Mario galaxy you simply need a comet medal. They are scattered in the worlds. There is one in most levels, other levels don't have any comet medals. If you get a comet medal in Yoshi Star galaxy you will get a prankster comet there later.
The purple comet is when you have to collect 100 coins in a 2 or 3 minutes. 100 PURPLE COINS!!!! Wow!
A comet one stupid.
I think its like a remix of Super Mario Galaxy's Purple Comet Missions.
A comet is in a solar system. A solar system is in a galaxy, so technically a comet is also in a galaxy.
They show up around certain galaxies when you get enough Comet Medals.
up the comets....
You can't. but you can unlock Rosalina that close enough To the SM1
When you get 120 stars you see a green comet and scatters 120 green stars