Red Boos, also known as Pink Boos, are a pink or light red variant of Boos. They aren't much different from the usual white Boos, except for their greater speed.
Red Boos first appeared in the "You vs. Boo" mode in Super Mario Bros. Deluxe, as the second fastest Boo the player races (the first being the Black Boo). They also appear in Super Mario Sunshine, where they are found haunting Hotel Delfino and Mario must drive them out.
After the basic white Boo became a playable character in the Mario Party games, the Red Boo took its place as a supporting character. In Mario Party 6 they act the same as normal Boos in earlier games, and steal coins or stars from players.
Red Boos make an appearance in the Mario Kart title, Mario Kart Silver. In the game, they appear as items that act exactly the same as the previous Boo items from other games in the series, in which they steal items from racers. Should, for whatever reason, no racer have an item, the Red Boo will disguise itself as a red, translucent Fake Item Box until someone does obtain one.