Mirror Mode is a Mario Kart: Double Dash!!, Mario Kart Wii, and Mario Kart DS Grand Prix mode. You unlock this from beating 150cc. The engines of the vehicles are 150cc, however every turn has been switched. Right-hand turns become left, and vice versa. Other fun tidbits include how words and signs are reversed, including your vehicle.
Related ThreadsMirror mode is really a mirror mode?? - last post by @ Jan 17, 2008
mirror mode questions - last post by @ Jan 18, 2009
Mirror mode on double dash - last post by @ Mar 16, 2010
How to beat mirror mode???!!! - last post by @ Mar 27, 2010
Mirror Mode??? - last post by @ Mar 16, 2010