Plains are one of the most common terrain types in the game. They give a small amount of terrain cover and are easily traversed.
Plains give one terrain star.
In Advance Wars 2: Black Hole Rising, Lash's ground units get a 10% attack boost on plains. In Advance Wars: Dual Strike, Jake's ground and air units get a 10% attack boost while Lash's ground units get a 5% attack boost.