The dash behind white and the kick/turn by white were amazing. Sweet particles. However, the reaction was way off. It looks like he eased into the flying backwards, stayed at the same speed for most of it, then slowed way down at the end as if the ground was repulsing him.
Realistic way: there should be no or very little easing at the beginning as the powerful force of the punch hits him, then backward motion decelerates as downward motion accelerates with the effect of gravity. Also, the flip at the end didn't make sense for the direction/speed he was going, maybe just a skid or something.
You've got to think of movement in 2 dimensions, with multiple forces acting on the stickman each with their own unique pattern of easing.
Also, it would flow better if you found something else for the black stickman to do besides standing there for half the anim.
Overall very smooth and great effects, no resizing, but physics are bad and very unrealistic.