Gratonios is a humanoid Warrior Beast with a mainly light and dark purple body. Its head has a light colored face with sharp teeth and a dark colored helmet with spikes and horns extending out of the helmet. Its pectorals feature a pair of faces resembling white and purple masks. Its hands are replaced with drills.

Gratonios is capable of short flight, its drill hands can extend for a short distance which is useful in close combat. The faces on its pectorals can act as shields and can shoot beams that can cause explosions from the eye sockets. Gratonios can also release electric shocks from the horns on its head.

Gratonios was launched along with Pilanias by Archduke Gorgon and the Great General of Darkness in their attempt to destroy Mazinger Z now that Dr. Hell was dead. Attacking the Photon Power Laboratory, the Warrior Beasts overpowered both Boss Borot and Diana A. Mazinger later arrives but it too stood no chance. When all looked hopeless, Great Mazinger appeared destroying Pilanias and later Gratonios with a Thunder Break.