Here are some hidden moves:

Neck Snap - Stand behind an opponent and press DOWN + B + A at the same time and Derrick will snap the opponents neck
Elbow punch with a Right Hook Combo - LEFT + B then A Ryu's Dragon Punch Uppercut - Up + B at the same time
Hammer Fist - DOWN + A then B Sliding Kick With a Dodge Roll - Up(Running) + B + A then LEFT or Right at the end of the slide