Well, as the title says, Wither Skeleton is unfinished. The reason I say this is because:

• If he kills you, it appear "<Player> was killed by entity.wither.skeleton"
• If he is in his attack mode, he will behave as the Normal Skeleton, like he was using an Bow, instead of use the Melee Animation. In fact, he will chase us to attack with his sword, but with the Skeleton Bow Animation.