Mazinger Z: Relic of Terror

An bonus chapter included with the final volume of Getter Robo Āḥ. Dr. Hell discovers a biomechanical lifeform known as "Kedora" in the depths of Bardos Island, and realises that he can use it to fight Mazinger Z.
The story of this chapter was loosely adapted into the sixteenth episode of Shin Mazinger Shougeki! Z-Hen.