Purple Coin

Purple Coins are special Coins that first appeared in Super Mario Galaxy. They will only appear in the regular galaxies when a Purple Comet is in orbit of a Galaxy.

Super Mario series
The player will always need to collect 100 Purple Coins to make a Power Star appear. Purple Coin Missions sometimes have a time limit. When there is a time limit, the Purple Coins are usually either set along a linear path, or over a hundred will appear and only one hundred of them will need to be collected. Additionally, once the Power Star appears, the player must collect it before the remaining time runs out.

In missions that aren't timed, the Purple Coins will be spread out across the level, requiring the player to explore every area in order to find them all.

There are two Purple Coin missions that are not activated by a Purple Comet. One is in the Gateway Galaxy and another in the Grand Finale Galaxy.

All of the timed Purple Coin Galaxies have a theme that is a remix of Gusty Garden Galaxy's theme. The Battlerock and the Dreadnought Galaxy have the same theme, but they do not have time limits.

Also, unlike the standard Yellow Coins, Purple Coins will not restore any of the player's health, nor refill the air gauge while underwater.

Purple Coins re-appear in Super Mario Galaxy 2. They still appear in Comet missions, however a small change has been made: the timer will stop once the requirements are met. In the Rolling Coaster Galaxy, a Purple Coin will be in a ball, replacing the Star Ball. This is called a Purple Coin Ball. Also to note in this game, Player 2 can collect Purple Coins for Player 1 along with Yellow Coins.

Mario Hoops 3-on-3
Slot Coins appeared in the stage Jr. Street. The player can get them by going on a purple ? Panel. It is used as money to make the Slot Machine of the stage spin after they scored.

Super Mario Galaxy Trading Card Description
''Purple Coins are special coins that only appear when a Purple Comet is in orbit of a galaxy. Mario must travel to each of these galaxies, collecting 100 purple coins in each one in order to reveal the Power Star that is hidden there.''

Trivia

 * Purple Coins were originally going to appear in Super Mario World, but became unused in the final version. They act like normal coins, but if a blue P-Switch is used, these coins will turn into pink Used Blocks but still act like coins.
 * Purple Coins are the possible successors to Red Coins from Super Mario 64, as Mario needs to collect a certain number of each to get a Power Star. Also, they could just be the successors of regular coins from the same game, as you need to collect 100 of either to get a star, and they both have stars on them.