You can unlock this during the end level boss, the witch, during level 4. Lower the witch’s health until the boss is almost dead. Then, when the witch shoots a missile at you, let it pass you. It will soon come back from the left side of the screen shooting to the right. Dodge the missile and let it hit the witch. If the missile kills the witch, the achievement will unlock. If the witch still has some health, let the witch shoot another missile at you and repeat the previous steps.