To obtain this achievement you have to go in the 8th level where you get your platypus for the first time. After defeating the enemies in the village grab a blue orb with your platypus and go in the “mage’s” room. Place the orb at the end of the room beside the door. Choose your dragon and burst the door. Now take the girl and use the mirror. Move your cursor behind the window so you can shoot the two torches with a single shot (Switch to the dragon and use the mirror to shoot). A door will open and the achievement is yours.