By pulling out a bomb at a relatively precise timing window, you can finish off Darkhammer with 1 Jump attack + Quickspin. The position of the bomb is not important.
In The Old Fixed EMS 100% Route, you have mortal draw you can finish Darkhammer in one hit with mortal draw. Make sure you are standing to the right of his tail so Link will definitely hit him.
NOTE: There are others way to make him throw the ball & chain such as waiting for 3 swings then rolling into him and pass him also makes him throw the ball & chain
After the Dark Hammer throws his Ball & Chain at you, use quickspins on his tail to quickly defeat him.