Red Coins are, as the name says, red-colored Coins. These coins are not just red coins, though. Red Coins are special coins that could give special things when all are collected. Most of the time, there are eight Red Coins scattered around a course. When collected in 3D Mario games, a Power Star appears somewhere.
There are also Red coins that only appear when a Red Ring is touched. These are rather closer than the normal ones, and also disappear after a small time. Also, when all eight collected, a Power-Up item appears, or a 1-Up Mushroom.
Red Coins appear in Super Mario Moose when a Red Coin Ring is touched. Collecting all 8 coins will reward the player with either a power-up or a 1-Up Mushroom.
Red Coins appear again in Super Mario Moose Deluxe, acting the same as in the previous game.