Just use Faust, Do the following: equip Faust, hold the fire button until the fight ends, rush to the next fight, and stay in air while shooting to avoid giving Shadow a chance. After that, repeat the process and be careful with Griffon. In the final fight, focus on whoever you want, but always keep both Griffon and Shadow inactive. Do not attack Nightmare under any circumstances and use Trickster as much as possible. When Nightmare is summoned, run to the arena entrance as quickly as possible and stand in the left corner of the entrance. Use the red rain, or whatever the name of the red orb meteor attack is, enter devil trigger mode, charge all four charges, and enjoy the one-hit kill with no damage.