Super Mario Galaxy/Ghostly Galaxy

Ghostly Galaxy is accessible from the Kitchen observation dome. You need 20 Stars to enter.

Star 1: Luigi and the Haunted Mansion
Once you rescue Luigi, he can be found in the Garage on the Observation Platform, from where he will help you find Hidden Luigi Stars.

Star 2: A Very Spooky Sprint
Race.

Star 3: Beware of Bouldergeist
Just before the boss fight, you will meet a Luma shop, who will sell you a 1-Up Mushroom or a Life Mushroom for 30 Star Bits. The Life Mushroom will probably be most useful for the upcoming fight.

Boss fight - Bouldergeist: Your object in this fight is to hit the body of Bouldergeist four times, using Bomb Boos. He will then regenerate and gain two hands, and you will need to bomb his main body four more times. He has a few attacks:
 * He will throw rocks at you, which you should evade. During the rock throwing attack he will also throw Bomb Boos, which you will need to collect and use to attack him.
 * He will make columns of rocks appear out of the ground. If you see a line of shadows appear directly below you, get out of the way to avoid being hit. Spin Attack the rocks to give yourself more space if necessary.
 * Once he has grown a couple of hands, he will try and attack you with them. You should avoid these attacks or hit the hands a couple of times with Bomb Boos to temporarily destroy them. Don't get too distracted by the hands, though - remember that you need to bomb the main body to defeat him.

Star 4 (Daredevil Comet): Bouldergeist's Daredevil Run
This Star is available when a Prankster Comet is in this Galaxy.

This is a repeat of the boss fight from Star 3, except you only have one life point.

Star 5 (Purple Comet): Purple Coins in the Bone Pen
This Star is available when a Purple Comet is in this Galaxy.

You need to collect 100 out of the total 150 Purple Coins, within a one minute time limit.

There are no coins on the initial planet upon which you land, so use the Pull Stars to navigate around. You haven't got much time, so try and go along paths where there are many coins in a row.

Star 6 (Hidden): Matter Splatter Mansion
Enter Star 2. Launch off the Shroomship. Spin Attack the higher of the two rocks, and use the Launch Star to reach a new area.

Here you will need to follow a 'spotlight', collecting keys to open doors, until you reach the Star.