I haven’t worked with the FX/sims part of production. What you’re describing is what is commonly referred to as jiggle physics or impact sim. A lot of the time this is done with creative weights painting, extra bones, and drivers. Sometimes it’s done with sims like cloth and/or soft body. There’s an addon called wiggle bones that is great for animating such actions. I can check my notes when I get home from work in about 8 hours. I don’t know if it will apply since it’s for 2.76, but it could be a good starter point.
