In Super Mario Galaxy, there are five different types of Prankster Comets, each one a different color: red, white, blue, yellow, or purple. They will appear from time to time in the orbits of the 15 major galaxies, starting at the point when Mario or Luigi collects his 13th Power Star. The missions can only be done if the player travels to a galaxy with a Prankster Comet in orbit. Prankster Comets will only appear in galaxies after a specific Power Star in any given galaxy is collected. Also, when a Prankster Comet is in orbit, the player is forced to choose its level. No option is given to choose "normal" levels. However, Comet Tico, who is positioned near the Terrace, will shuffle the comets between available galaxies if fed 20 Star Bits by the player. It will either remove all comets from orbiting in galaxies, remove some of them, or make some appear.
By completing the event, the player will receive a Power Star. While a Prankster Comet is in orbit of a galaxy, players will need to completely restart the level each time they lose a life, instead of coming back at the last checkpoint. 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 the Prankster Comets (except some Purple Comets) also have their own music that plays during their missions.
In Super Mario Galaxy 2, Prankster Comets only appear once the player has collected a Comet Medal in a certain galaxy, as well as a certain number of those from other galaxies. In this game Prankster Comets with different effects are no longer considered different types of Comets. Galaxies under the influence of a Prankster Comet are given a generic symbol. Below, the Super Mario Galaxy 2 comets are grouped together based on the title of the mission they appear in. Comets are now yellow if they give Power Stars, while green if they give Green Power Stars. Traveling to a galaxy with a comet in orbit opens up the comet Star mission, although the player may have the option to select a normal mission, unlike in the first game. Also, a Prankster Comet will always be in orbit around a galaxy once unlocked, unlike in the first game, where completing a mission could move the Prankster Comet to another galaxy. Certain galaxies (Fluffy Bluff Galaxy, Boo Moon Galaxy, etc.) do not have Prankster Comets.
The Speedy Comet requires the player to complete a level within a certain time limit, from four to six minutes. Also, there will be small changes in the galaxies. For example, Good Egg Galaxy's boulders are all replaced by Chomps. Four galaxies are visited by the Speedy Comet: the Good Egg Galaxy, Space Junk Galaxy, Dusty Dune Galaxy, and Dreadnought Galaxy.
This comet also appears in Super Mario Galaxy 2. A list of galaxies visited by it includes the Sky Station Galaxy, Bowser Jr.'s Fiery Flotilla, Hightail Falls Galaxy, Bowser's Lava Lair, Rolling Masterpiece Galaxy, Supermassive Galaxy, Bowser's Gravity Gauntlet, Throwback Galaxy, Bowser's Galaxy Generator, the Stone Cyclone Galaxy, and the Boss Blitz Galaxy. Unlike the previous game, the Speedy Comet in Super Mario Galaxy 2 can dramatically change the original level in addition to setting a time limit, e.g. Hightail Falls Speed Run has damaged platforms and meteors, and Masterpiece Speed Run has an entirely new planet not seen in the original star mission as part of the level.
Galaxies marked with * next to their time limits have Timers scattered throughout the mission; collecting one adds 10 seconds to the player's time limit.
The Daredevil Comet cuts Mario or Luigi's maximum health down to only one hit point, as opposed to the usual three (or six with a Life Mushroom). Additionally, it removes all Life Mushrooms and even coins from the level so that the player cannot get them. Five galaxies are visited by the Daredevil Comet: Battlerock Galaxy, Ghostly Galaxy, Gusty Garden Galaxy, Deep Dark Galaxy, and Melty Molten Galaxy. Four of them have the player battle a previously fought boss: Topmaniac, Bouldergeist, Major Burrows, and Kamella respectively, with the sole exception being Melty Molten Galaxy, which has the player complete the entire first mission (The Sinking Lava Spire) with only one hit point. Taking any damage during a Daredevil Comet will require the player to start the mission over from the beginning. At the start of the first four aforementioned galaxies, the player will automatically be brought to the last planet where the boss resides, without the need to travel throughout the galaxy.
The Daredevil Comet is also in Super Mario Galaxy 2 in Spin-Dig Galaxy, Bowser Jr.'s Fearsome Fleet, the Slipsand Galaxy, Bowser Jr.'s Boom Bunker, the Battle Belt Galaxy, and the Grandmaster Galaxy. Unlike the original Galaxy, however, some of the Daredevil Runs in Super Mario Galaxy 2 have Checkpoint Flags. Just like the Speedy Comet, the original level can be dramatically changed when visited by a Daredevil Comet.
The Cosmic 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. If the player uses Luigi, they will be racing against Cosmic Luigi instead. Unlike Cosmic Mario, Cosmic Luigi long jumps frequently and takes advantage of some shortcuts that are available. Cosmic Comets only appear in Super Mario Galaxy, being replaced by Clone Comets in Super Mario Galaxy 2.
The Fast-Foe Comet speeds up all enemies and obstacles in a stage. Mario must complete the stage while avoiding the accelerated enemies and obstacles. Only two galaxies are visited by the Fast-Foe Comet: the Beach Bowl Galaxy, and Toy Time Galaxy. Tox Boxes, Thwomps, and moving platforms are the only objects affected. Fast-Foe Comets only appear in Super Mario Galaxy, being replaced by Double Time Comets in Super Mario Galaxy 2.
The Purple Comet is only available after the main story is beaten. Purple Coins are hidden throughout the galaxy, and Mario must retrieve at least 100 Purple Coins, sometimes within a time limit, to retrieve the Star. Some Purple Comet missions have more than 100 Coins, but Mario still only needs to collect 100 for the Star. All 15 major galaxies are visited by the Purple Comet. Timed Purple Comet missions, as well as the Battlerock and Dreadnought Galaxy's Purple Comet missions, use a unique background music, which is a remix of the Gusty Garden Galaxy music.
There are also Purple Comets in Super Mario Galaxy 2. They are the same as Super Mario Galaxy but, instead of having to beat the game for Purple Comets to come, only the Galaxy's Comet Medal is required. The mission in Starshine Beach Galaxy plays the Hightail Falls Galaxy music, since the Dash Pepper is needed to clear, even though the normal level has a Dash Pepper and using it won't change the music. The specific Purple Coin theme music from the first game plays in the Flip-Swap Galaxy, Puzzle Plank Galaxy, Clockwork Ruins Galaxy, and Mario Squared Galaxy.
The Clone Comet replaces the Cosmic Comet from the first game. Multiple Cosmic Clones appear on a selected mission. The player needs to redo the whole or part of the mission while there are Cosmic Clones. The comet appears in the Cloudy Court Galaxy, the Haunty Halls Galaxy, the Chompworks Galaxy, and the Flip-Out Galaxy. It is fused with the missions Purple Coin Shadow Vault for Puzzle Plank Galaxy, Luigi's Purple Coin Chaos for Mario Squared Galaxy, and Green Star 2 for Flip-Out Galaxy. The specific music for the Cosmic Clones theme does not play (except Cloudy Court Galaxy) even though the soundtrack stays the same. This music is also played in other stages such as Stone Cyclone Galaxy. Clone Comets only appear in Super Mario Galaxy 2.
The Romp Comet requires Mario to defeat a horde of 30 enemies within a time limit using a power-up, with the exception of the Flash Black Galaxy, where no power-up is given. This comet appears in the Yoshi Star Galaxy, the Boulder Bowl Galaxy, the Flash Black Galaxy, and the Shiverburn Galaxy. Romp Comets only appear in Super Mario Galaxy 2.
Double Time Comet
The Double Time Comet makes the player redo a level, this time with the hazards moving faster. It appears in Beat Block Galaxy and Twisty Trials Galaxy. This is similar to the Fast Foe Comet from the first game, except that instead of enemies, the stage hazards move faster, and slightly slower overall than when a Fast Foe Comet is in orbit. Despite being called the "Double Time Comet," the objects actually move at four times the normal speed. Double Time Comets only appear in Super Mario Galaxy 2.
The Green Comet makes Green Stars appear in various levels in every galaxy except the Grandmaster Galaxy, usually in hidden or hard-to-reach places. There is one Green Star for every normal Power Star mission; galaxies with two missions have two Green Stars to find, and galaxies with three missions have three Green Stars to locate. In either case, Green Power Star levels are always named as "Green Star 1" and "Green Star 2" (as well as "Green Star 3" for galaxies with six Power Stars total) as opposed to being named in the same way as normal galaxy levels. Green Comets only appear in Super Mario Galaxy 2.
Names in other languages
Speedy Comet (Super Mario Galaxy)
Daredevil Comet (Super Mario Galaxy)
Cosmic Comet (Super Mario Galaxy)
Fast-Foe Comet (Super Mario Galaxy)
Purple Comet (Super Mario Galaxy)