Ghostly Galaxy

The Ghostly Galaxy is a galaxy in Super Mario Galaxy where Mario turns into a Boo with the Boo Mushroom. Pink Boos, UFO spinning tops with Bob-ombs on them, Swoopers, Cosmic Scuttle Bugs, and Pumpkin Heads have been spotted in screenshots. This galaxy also has the first appearance of Luigi in the game.

Enemies

 * Boos
 * Swoopers
 * Pumpkin Heads
 * Goombas
 * Bomb Boos
 * Chomp Heads
 * Cosmic Scuttle Bugs

Luigi and the Haunted Mansion
At first, Mario starts off on the Toad Brigade's ship, but has to use a Launch Star to reach the pathway into the mansion (the toads most likely to scared to go farther). Pumpkin Goombas litter the pathway, so Mario must be careful. Boos are inside the mansion, but a switch activates a swinging beam of light, which Mario has to lure them into to defeat them and get the items they are guarding. One of the Boos has a key to get deeper into the mansion.

Soon, there are Star Chips to collect to rebuild a Launch Star which will then be located in one of the windows a black hole was. Using the Launch Star, Mario is then launched into another part of the mansion, where Luigi is calling for help, but a window makes it impossible to help Luigi. Mario will have to find another way inside, where he discovers a new power-up, the Boo Mushroom. As Boo Mario, he needs to vanish to pass through the bars, but he must be careful as a beam of light which will make him lose the Boo Suit is in the next area. Mario needs to return to normal before he can speak with Luigi to get the Power Star.

A Very Spooky Sprint
In this level, Mario must blast to the edge of the galaxy and race the Spooky Speedster, through an area that looks like the Bone Pen.

Beware of Bouldergeist
Mario is informed by a member of the Toad Brigade that Luigi has been kidnapped by "The monster that lives up ahead". Mario will have to find his way to a circular stone platform and then meets Bouldergeist, a ghost with the ability to control stone. Mario will have to defeat Bouldergeist with Bomb Boos. After taking an amount of damage it eventually explodes, leaving behind a Power Star.

Bouldergeist's Daredevil Run
Very similiar to Beware of Bouldergeist, however Mario starts on the boss planet with a health max. of 1. This mission, until completed, is only available while a Daredevil Comet is in orbit. It is a very hard star to get since there are many ways to get hurt.

Purple Coins in the Bone Pen
Mario starts off on a small planet with the "Bone Pen" in front of it. The Bone Pen features bones as walls, meaty bones as bumpers, spiky balls as obstacles, and Pull Stars for getting around. Thre are more than 100 Purple Coins, but 100 have to be collected by the player before the Power Star appears in the center of the pen. This mission, until completed, is only available when a Purple Comet is in orbit, and has a one minute time limit.

Matter Splatter Mansion
A mission similar to the Matter Splatter Galaxy. While playing the level "A Very Spooky Sprint", the ring shaped planet containing pumpkin-headed Goombas also has two breakable stalagmites. One contains a Rainbow Star, and the other contains a Launch Star to the Matter Splatter Mansion (there is a sort of light around the one with the launch star). Platforms and rooms only exist when a sort of "Spot Light" comes over them. The Player will need to go through, getting keys, and unlocking doors to get through, until, eventually, there will be a Power Star behind one of the doors.

Trivia

 * In the level "Beware of Bouldergeist", a Toad at the beginning of the level said Bouldergeist kidnapped Luigi, although Luigi does not make an appearance in the level. It is assumed, however that Bouldergeist is the creature that brought Luigi to the Ghostly Galaxy, as seen it the first level,"Luigi and the Haunted Mansion".
 * The level "Luigi and the Haunted Mansion" is an obvious reference to "Luigi's Mansion".
 * Strangely, when the player is Luigi, The trapped Luigi still shouts 'Mario'. This may have been something the developers missed, or Luigi was expecting Mario to come and not himself.