Ghost (Super Mario Galaxy 2)
A ghost is a helpful character that appears in Super Mario Galaxy 2. A ghost can be created at any point in the game, but it is created only when the player successfully completes any mission in a galaxy while playing as Luigi instead of Mario or by having 9,999 coins in the coin collection on Starship Mario, which causes a ghost to appear in all galaxies, all missions leaving no need to play as Luigi. For this reason, it is considerably easier for the player to create ghosts after Mario has defeated Bowser in Bowser's Galaxy Generator at the end of the game, as Luigi then appears onboard Starship Mario and is available for the player to use at any point. Before that point in the game, ghosts can be created only if the player agrees to let Luigi take over a particular mission when he appears at the starts of some galaxies. Therefore, the player has more control over where and when ghosts are created later in the game, as opposed to earlier in the game.
After the player completes a mission with Luigi and returns to Starship Mario, the player receives a message saying that a ghost has appeared in the galaxy from which they just came. The ghost that is created always takes the form of a translucent Luigi, and it never takes the form of Mario. Once created, a ghost can be found at the starting planet/area of each galaxy for which the player has followed the procedure to create it. To activate the ghost, the player must have either Mario or Luigi touch it as it runs in place near the start of a galaxy, after which it takes off running through the galaxy, leaving a trail of green arrows on the ground behind it. Should the player ever lose sight of the ghost while it runs through the galaxy (as it does move considerably faster than Mario), they can use those arrows to track the ghost's previous movements.
The ghost usually takes any and all available shortcuts while running through a galaxy, even when they are not readily apparent to the player. This is because the ghost reflects the actions of some of the game designers as they had gradually completed the galaxy themselves, much like the actions of a staff ghost in Mario Kart Wii. Depending on the mission in a galaxy, the ghost may either lead the player to the Power Star at the end of the mission or lead the way to a hidden Comet Medal in the galaxy. If the ghost leads the way to a Power Star, it jumps up into the air where the Power Star is and grabs on to the bottom of it, turning around with the Power Star as it rotates in midair (if the Power Star has not appeared yet, it merely hovers in the air until it does, at which point it grabs on to the Power Star). If it leads the player to a Comet Medal, it lies down on the ground under or near the Comet Medal, and it does not move for the remainder of the mission. Alternatively, the ghost may lead the player to neither of those locations, in which case it simply runs to a hard-to-reach area, then lies down on the ground and relaxes.
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