Its armor minimizes the damage it takes, and it is almost impossible to stun until you yank off its helmet with the Oraclos Chain.
It attacks by launching its 'mace' at you or spinning it around and walking towards you. By spinning it around it stops the chain from getting to its body. Attacking from the back will make him stop.
There are three places the chain can latch on to: The mace (only when dead), the hand and the helmet (or head when the helmet is off.)
If you bind his arm, the Skull Knight will make you trip by tugging on the chain, leaving you open for attacks.