Luigi and the Haunted Mansion

"We detected signs of Luigi in this galaxy! I hope he hasn't been eaten by ghosts!"

- Toad

Luigi and the Haunted Mansion is the first mission of the Ghostly Galaxy in Super Mario Galaxy. The primary goal of this mission is to rescue Luigi from a haunted mansion. Once this level is cleared, Luigi sends Mario letters with him finding Power Stars.

Layout
The player starts off on a Starshroom and has to use the Launch Star underneath to reach the mansion. The gate of the mansion has three Pumpkinhead Goombas and a Sprangler, along with a Rainbow Star found in one of the spires. The stone walkway to the mansion twists and has a Chomp rolling down it.

The interior of the mansion has several statues of Bowser and a couple of Boos. By flipping a Lever Switch, the player can turn on a light that can defeat the Boos, and defeating the one that comes out of the portrait at the top of the stair will yield a Key that will open the door to the next room. The next room is a large cube with many Pumpkinhead Goombas and Star Chips containing three black holes where the windows are supposed to be and the gravity is affected by moving along the ramps. Ground Pounding on the broken roof will take the player to a secret library where the player can collect a number of Coins.

By collecting all the Star Chips, the Launch Star will form, which will launch Mario around to the exterior of the mansion where they can meet Luigi. By using Pull Stars to collect a key, the player is able to enter the next room full of Boos. By touching a ? Coin, the player can cause a Boo Mushroom to appear, which will turn Mario into Boo Mario. Using the power-up to phase through walls and avoiding lights, Mario can reach Luigi and rescue him, earning a Power Star. However, Luigi will only talk to Mario if he isn't a ghost, so Mario has to first turn back to normal using a light. If Mario approaches Luigi in Boo form, Luigi will hide his face in fear.

Trivia

 * The level is an allusion to Luigi's Mansion, since Bouldergeist captured Luigi and Mario has to rescue him, taking place in a haunted setting with a mansion, although the roles of Mario and Luigi have now been inverted.