Red Coins are items in Luigi's Mansion: Dark Moon. They only appear in secret areas and after completing a floor in ScareScraper. Unlike the typical Coins in the Luigi's Mansion (series), these coins are big, red, floating coins that do not count toward the treasure count.
Obtainment[]
Dark Moon Quest[]
In the Dark Moon Quest, Red Coins will only appear in pocket challenges found within the Paranormal Dimension, which are usually found in certain objects in certain missions, and they are usually in the form of some type of maze. To win the secret room, Luigi must collect all the Red Coins in the time given. Usually this is not hard, as the coins are given in a straightforward manner, however the time limit is a difficult part of these rooms. After collecting all the Red Coins, a chest will appear in the middle of the room, usually containing treasure, or sometimes Gems. If Luigi fails, he will be teleported out of the room and back to where he was, and he cannot try again unless he redoes the mission in its entirety.
ScareScraper[]

As a result of collecting Red Coins in the ScareScraper, one of the Luigis will receive a power-up to aid them in the upcoming floor.
In ScareScraper, Red Coins only appear after completing a floor. There will only ever be four of them at once, and they will appear in random rooms. The Luigis must collect these coins if they want an item to help them in the next floor. Since only one Luigi can have the item, the more Red Coins a player collects, the higher the chance of them getting the item. At the stats screen at the end of a floor, a roulette will determine who gets the item by landing on the face of the winning Luigi, and having Red Coins will increase the chance of winning by adding another face per coin, for the player that collected the coin.