Not a part of the official blazon (except that sometimes the colors are specified), the mantling varies with the herald's or artist's preference. This is said to represent the bearer's cloak, even though it may often look more like the leaves of a plant.
Note: Helmets, banners, and shields are not a part of the mantling, and these elements can all be mixed and matched. The colors and special effects can easily be changed!
Other mantlings can be used, but this would qualify as original artwork.