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
You'll be surrounded by three bats that ram you, so avoid it! There's no mansion, just use the pull stars and the launch star on front of the mansion.

You'll see a boo with a helmet on it, and it wants you to race in order to get a power star.

You'll be in a racing alley with lots of bones and skulls. Don't let go of a pull star or you will fall to the beginning. And don't hit a bone with meat in it or you with bump into it and it will make you slower. At the final part, it has mines in it, but don't even panic, avoiding them makes you slower. Destroy two of the mines, but when you fall, try catching another pull star. When you get on the planet, quickly get on top of the planet to win.

Star 3: Beware of Bouldergeist
Beware of this planet, there are too many enemies, so spin into a stone and get a Rainbow Star. Run the three bats into the planets, get on front of the bridge and run into the three purple spiders, and quickly get into the bridge and destroy the chain-chomp. But then it's easy to already lose the rainbow star, so either try to kill the three bats near the bridge or run into the mansion.

You'll now see a frame of a weird-looking boo. It's called a Bomb Boo. With Bomb Boos, spin into one on time to swing them around to explode a breakable thing. You can also see Bowser statues, and they are breakable. You see the Bowser statue blocking the fireplace? Destroy that and there is a Launch Star.

Now there are more spiders than ever. When the brown spider jumps, quickly get past it before it comes down. Then spin into it. Next, beware of the two purple spiders: they can swing to touch and hurt you, so for the first one: spin it two times, and do the same to the other one. Now there is a moving platform with a purple spider under a sling pod: don't let it push you off. Stun it while on the platform and get on the sling pod.

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. Try to not stand still for a second, just always move into a line of purple coins so that you can get 100 coins collected quickly.

Star 6 (Hidden): Matter Splatter Mansion
Enter Star 2. Launch off the Shroomship. Spin Attack the higher of the two rocks (it will be slightly shining), 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. Boos will follow you for some time while you do this. While following the path, repeatedly Spin Attack in order to continue moving the Boos around, as you will be unable to defeat them properly.