Grendizer, Getter Robo G, Great Mazinger: Kessen! Daikaijuu(グレンダイザー・ゲッターロボG・グレートマジンガー 決戦!大海獣,Gurendaizā Gettā Robo Jī Gurēto Majingā Kessen! Daikaijū, Grendizer, Getter Robo G, Great Mazinger: Battle! Giant Sea Beast) is an animated film produced by Toei which premiered originally in July 18, 1976 (1976-07-18) in Japan. It is a crossover of three super robot anime: Grendizer, Getter Robo G and Great Mazinger. Like the rest of the Vs. animated films of Toei, the movie features alternate versions of events from the three series and is not canonical to any of them. The film was released in almost all countries where the original Grendizer series was broadcast. It is known as Il Grande Mazinga, Getta Robot e Goldrake contro il Dragosauro in Italy and Goldorak: L'attaque du Dragozaure in France and some parts of Canada.
The Dragosaurus, a mysterious prehistoric animal, surviving unknowingly in the depths of the oceans, seeds panic by devouring huge quantities of oil around the planet, until it starts to head for Tokyo. However, despite this Japan has some aces in his sleeves: Grendizer, Great Mazinger and Getter Robo G, which are immediately sent to stop the monstrous animal. Unfortunately, the awkward Boss Borot joins the team and ends up being swallowed by the Dragosaurus rendering all more difficult. Boss Borot eventually manages to escape the creature's stomach thanks to Great Mazinger. As the three super robots try to fight off Dragonsaurus the animal makes its way to Tokyo and goes on a rampage. Dragonaurus is eventually killed off after Getter Robo G uses the Shine Spark to ignite the large quantities of oil in its body, saving the city.
The main antagonist of the film, the Dragonsaurus is an ancient reptilian animal that grew to large sizes from the oil it consumes with maximum size being 550 meters and 40,000 tons. Dragonsaurus is armed with seven serpent-like tentacles that can extend very long distances and are used as its primary attack. Dragonsaurus also has extremely potent regeneration that allows it to regrow its seven serpent-like tentacles in a matter of seconds and is strong enough to make it extremely resistant if not immune to electric attacks like Double Spazer's Cyclone Beam and acid attacks like Grendizer's Melt Shower. Dragonsaurus's body also has a high resistance to beams and absorbs projectiles such as missiles through its skin where they fail to detonate. To move on land Dragonsaurus possesses the ability to levitate, but also uses its tentacles to create hurricane-force winds.
Dragonsaurus later appears in various Super Robot Wars titles as a boss and in Super Robot Wars Reversal and Super Robot Wars MX is given a powerful sonar attack.
Production: Studio: Toei Doga, Dynamic Planning
Original work: Go Nagai, Ken Ishikawa, Dynamic Production
Director: Masayuki Akechi
Assistant director: Kazumi Fukushima
Animation director: Tatsuji Kino
Scenario: Susumu Takahisa
Planning: Ken Ariga, Katsuya Oda
Producer: Chiaki Imada
Executive producer: Saburo Yokoi
Art director: Mataharu Urata
Music: Shunsuke Kikuchi, Michiaki Watanabe
Theme Song: "Izaike! Robot Gundan" (いざ行け! ロボット軍団,Izaike! Robotto Gundan, translated as "Now go! Robot army") (lyrics by Kogo Hotomi)
Theme Song Performance: Isao Sasaki, Columbia Yurikago-kai