Quickly allows you to assign different falloff shapes to the sprite’s color value.
The options are Square, Round, Star, Dot, Ring, Horizontal, Vertical and Z.

Storm Tracer Falloff shapes from left to right : Square, Round, Star, Dot, Ring, Horizontal, Vertical, Z
Z mode utilizes the Z-Depth to create quite fog shading effects but also shades as if the sprite were a sphere.