Fanbeichui can be called 'backfist' in English. It comes from deeper down in the body than the usual backfist. One of our association members is known for knocking out a thief twice his size with this technique.
It is unique in that it uses a fist. It is used along with stepping to apply a technique when it seems like the back is turned to the opponent.
Eagle way of doing fanbeichui
Power release drills
Partner training drills
Sparring drills