Dragon Ball Z: Lord Slug (1991)

During a carefree moment, Gohan and Piccolo feel a powerful entity approaching. Soon it is discovered that it is a planet that is transforming itself into a castle near the Earth, from which a large army is emerging, which declares that it is now in the possession of Slug, an evil Namekian who wants the Dragon Balls to restore his power from his youth. This film takes place at the beginning of the Namek arc., before the fight with Frieza.