When you've released the darkness in his dreamworld you need to defeat him some way to get control of him. What i did was when i interacted with the 4 strange stair thingy's the darkness was released. then i ran back and sit in a corner so i didnt get hit by his Black Hole. If you stay in the corner he only sends some beserkes. 2 atta time. just kill the beserkers till he stops attacking you. at that point walk up to him and press A to suck up the darkness. This time you control it according to the storyline.

Note: DO NOT SHOOT AT HIM, he only gets stronger if you do. just keep killing his beserkers and now and then cap a bullet in his body to make him active again, cuz he tends to do nothing when sitting in the corner. show your face once a while.