Defeating him the first time will net you the Majel Robo, the Indigo Gun, Indigo Bomb, Indigo Pod, and Indigo Legs, as well as a pass that will allow you to access the underground. After defeating the Greybaum enemies with the boss data, you can again fight the doppelganger. This time, he will give you the Ray II Dark Robo, Ripple Laser Gun, Deva Bomb, Cerberus Pod, and Phantom Legs.
Defeating him the first time will net you the Majel Robo, the Indigo Gun, Indigo Bomb, Indigo Pod, and Indigo Legs, as well as a pass that will allow you to access the underground. After defeating the Greybaum enemies with the boss data, you can again fight the doppelganger. This time, he will give you the Ray II Dark Robo, Ripple Laser Gun, Deva Bomb, Cerberus Pod, and Phantom Legs.