The Wave is one of the few cards never used in the manga (which only had nineteen Clow Cards) or anime. It has the ability to create gigantic tidal waves and to control the ocean currents. It is able to control water near it, but is unable to create new water like The Watery can. It can be combined with The Watery for a deadly effect.
The Wave is under The Watery Card.
The Wave is transformed into a Sakura Card in Episode 53 during Sakura's frantic wave of transformations.