The Red Key is a key item that appears in Wario: Master of Disguise.
The Red Key, as the same states, is a key that is red in color and Wario describes it as shiny.
The Red Key is one of three keys found in Allergia Gardens (along with the Blue Key) and Yellow Key). It can be used on two different doors of the same color. The Red Key can be found in a purple treasure chest in a room with a bunch of red mushrooms that are used to activate platforms.