After losing around 50% of health, Rhode will crouch down as black blood splashes from his body. Several warriors will be raised from their dead to fight you. So all you need is to do is run around closer to those warriors. Rhode will use long distance attack at your direction. The blast from his long rang attack would kill these warriors. After surviving the first wave, damage the boss until he summons dead warriors again. You should be able to have Rhode kill 10 warriors on the second waves.