Dragon Ball Z - Fusion Reborn (1995)

A teenage ogre, distracted by his heavy metal music, accidentally breaks an important "evil purification" machine in the Otherworld. A giants rift opens between the Otherworld and Earth, and the dead--including many old Dragon Ball villains and even Hitler--cross over into the land of the living. Even the wish-granting powers of Shenlong the dragon are insufficient to close the gateway, and Gohen, Goten, and Trunks must battle the undead hoards. Meanwhile, their deceased fathers Goku and Vegeta, already dead and in the Otherworld, attempt to repair the faulty machine, but discover that the young ogre has been transformed into a monster named Janenba that has strange powers and seems invincible to their mightiest attacks. As a last chance, Goku must convince Vegeta to swallow his pride and use the Fusion Dance technique.