Prankster Comet

Prankster Comets are Comets that appear in Super Mario Galaxy. They will appear from time to time in the orbits of various galaxies. If the player travels to a galaxy when a Prankster Comet is in orbit, a special event will be triggered, which will usually change the gameplay of the level. Also, when a Prankster Comet is in orbit, the player is forced to choose its level. No option is given to choose "normal" levels. By completing the event, the player will receive a Power Star. While a Prankster Comet is in orbit of a galaxy, the Player will need to completely restart the level each time they die, instead of coming back at the last check point. Once a Prankster Comet's star has been collected, its star will become a selectable mission, only causing the comet to return to the corresponding galaxy at the player's request. All of the Prankster Comets also have their own music that plays during their missions.

Prankster Comets

 * The Speedy Comet (レッドコメット Red Comet)  requires Mario to complete a level within a certain time limit, usually from 4 to 6 minutes. Also, there will be a small changes in the galaxies. Good Egg Galaxy's boulders are all replaced by Chomps; Space Junk Galaxy has several coins placed on planets; Dusty Dune Galaxy has all its enemies except the five Pokey Sprouts, the Pokey and the boulders; Dreadnought Galaxy has one Spiked Topman where there was a Spring Topman.  Four galaxies are visited by the Speedy Comet; the Good Egg Galaxy, Dusty Dune Galaxy, Space Junk Galaxy, and Dreadnought Galaxy.
 * The Daredevil Comet (デスコメット Death Comet) sets Mario's max health to only one unit, as opposed to the usual three (or six with a Life Mushroom). Five galaxies are visited by the Daredevil Comet; the Battlerock Galaxy, Ghostly Galaxy, Gusty Garden Galaxy, Deep Dark Galaxy and Melty Molten Galaxy. Four of them have the player fight a previously fought boss, with the sole exception being Melty Molten Galaxy, which has the player complete the entire first mission (The Sinking Lava Spire) with only one health unit.
 * The Cosmic Comet (シャドウコメット Shadow Comet)  pits Mario in a race against Cosmic Mario in a predetermined course with a star at the end. Mario must beat his duplicate to the Star. Four galaxies are visited by the Cosmic Comet; the Honeyhive Galaxy, Freezeflame Galaxy, Gold Leaf Galaxy, and Sea Slide Galaxy. Hint: To get a head-start in front of Cosmic Mario, the player can hold forward on the Nunchuk, and when the timer reaches 2, press Z and Mario should turn yellow giving him an advantage.
 * If the player is playing as Luigi, he/she will be racing against Cosmic Luigi instead. Unlike Cosmic Mario, Cosmic Luigi is more intelligent, and will take advantage of any shortcuts that are available.
 * The Fast-Foe Comet (クイックコメット Quick Comet) speeds up all enemies in a stage. Mario must complete the stage while avoiding the accelerated enemies. Only two galaxies are visited by the Fast-Foe Comet; the Beach Bowl Galaxy, and Toy Time Galaxy. Only Tox Boxes and Thwomps have been affected by this comet. The moving platforms also move faster.
 * The Purple Comet (パープルコメット Purple Comet) is only available after the main story is beaten. Purple Coins are hidden throughout the galaxy, and Mario must retrieve one hundred, sometimes within a time limit, to retrieve the Star. Some Purple Comet missions have more than one hundred Coins, but Mario still only needs to collect one hundred for the Star. All fifteen "main" galaxies are visited by the Purple Comet. Timed Purple Comet missions, as well as the Battlerock and Dreadnought Galaxy's Purple Comet missions have unique background music, which is a remix of the Gusty Garden Galaxy music.