Debris and such effects get different treatments by me at different times. For these embers I used a slanted hard brush for creating the shapes and then applied a motion blur. Sometimes I will use a softer brush with no blurs if I'm painting flying rock or debris. It kind of depends on the material and the speed you want it to appear to travel.
Congratz on the win. I really love the embers you placed in the fore ground. Really gives a sense that everything is burning where these two are duking it out.