After defeating Giant False Ridley and reviving the real one. Ridley then proceeded to explain what had happened, but couldn't as the configuration of his vocal cords made speaking English incredibly difficult. Mewtwo, who is telepathic, volunteers himself as a translator. After this explanation, you have the rest of the level, which thankfully isn't that long. After you complete the level, everyone from Group B joins your party(so does Ridley if you went through the door and defeated his giant doppleganger).