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.

Prankster Comets

 * The Speedy Comet requires Mario to complete a level within a certain time limit, usually from 4 to 6 minutes. Four galaxies are visited by the Speedy Comet.
 * The Daredevil 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. 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 with only one health unit.
 * 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 Fast-Foe Comet speeds up all enemies in a stage. Mario must get to the end while avoiding the accelerated enemies. Two galaxies are visited by the Fast-Foe Comet.
 * The 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.