Description:

A giant sea monster known as "Dragonsaurus" has emerged from out of nowhere, terrorizing the depths of the oceans. Great Mazinger, Grendizer and the Getter Robo G team join forces to combat the new threat. But their task becomes more complicated when Dragonsaurus swallows up Boss Borot and makes its way toward Tokyo. (Source: ANN)

Alternative Titles:

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, Grendizer: Getter Robo G - Great Mazinger Kessen! Daikaijuu