Big Sleep is one of Sandman's lackeys and quite a tough one at that. He is only encountered when you fight Sandman and he will likely be the tougher enemy of the two.
He uses his anchors in a variety of ways during combat. At first, he'll swing them around like clubs and try to hit you with them but he can also whip them at you long range similarly to the blades from God of War. He'll swing them both over head and then bring them crashing down on top of you. If he happens to hit you with them, he'll pull them back to him and you'll come with them. Sometimes it will put you right in front of him while other times you will simply fly in his general direction and go over his head.
There's no easy way of defeating him except by hitting him in the body. The best method is to use powerful bursts of damage like from a shotgun, sniper rifle, or rocket launcher. He can block shots by crossing his anchors in front of him but he won't do this until after you've hit him a few times. For this reason, you want to do as much damage as quickly as possible before he can bring his guard up. Then you wait for him to lower his guard and do it again. Repeat this process until he goes down.