Red-Hot Purple Coins
From the Super Mario Wiki
Red-Hot Purple Coins is the fifth mission of the Melty Molten Galaxy in Super Mario Galaxy. Until its completion, this mission can only be done while a Purple Comet is in orbit. This Purple Coin mission has no time limit.
A total of one hundred Purple Coins are placed around the starting planet of the galaxy. They are usually placed in groups and can be found over lava and under sinking platforms as well. Once all of the Purple Coins are collected, the Power Star will appear on the highest platform.
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