The new Shape operator, which replaces the original version, expands the choices of ready-made geometry for use in the particle system. You can specify particles in a number of different predefined 2D and 3D shapes, such as geometric primitives, alphanumeric characters, and musical notes, as well as particle size and scale.
The Shape Facing operator creates each particle as a rectangle that always faces a particular object, camera, or direction. For effects like smoke, fire, water, bubbles, or snowflakes, use Shape Facing with a material containing appropriate opacity and diffuse maps.
Shape Instance lets you use any in the scene as particles. You can effectively define only one reference object per event, but the object can comprise any number of sub-objects, each of which Particle Flow can treat as a separate particle. Also, using tests, you can divide the particle stream into multiple branches and define a different particle shape for each.
Use the Shape Mark operator to replace each particle with either a rectangle or a box cut out from the particle geometry with an image mapped onto it. The image can be animated and the animation can be synchronized with particle events.