The Black Cerberus fight has 2 phases. In the first phase you fight against the Black Cerberus and in the second phase you fight against a robot like P.A.X, the first boss in the game.
The 2 phases are repeated over and over again depending on damage done and/or time. Black Cerberus regenerates health in the robot phase. If it takes you too much time he will regenerate a lot of health. You have also a limited time during the fight against Black Cerberus and after a while he calls the robot and is hiding.
During the Black Cerberus fight dodge the attacks and wait that the attacks are over and hit Black Cerberus with your weapon 1 or 2 times and then dodge again the attacks and wait.
The robot phase is a little bit tricky. For the entire fight you have to hide under the roboter or he will hit you massivly. To force the robot to its knees so that you can do damage you have to do 2 things. At first remove the armor from the robots legs. After you destroy the armor the robot lifts one of his two legs. If one leg is in the air hit the other leg to force the robot to kneel down. For this step I use a fast weapon.
Kill the robot and the Black Cerberus enter the room again, rinse and repeat the steps until Black Cerberus is down.