In this epic conclusion to the Super Dragon Ball Heroes arc, Goku and Vegeta fuse together to become Gogeta, the ultimate warrior of the universe. Their combined power provides a big enough zen-ki boost to battle Hearts who seems invincible.
Gogeta’s power is incredible and completely overwhelms Hearts. With the help of two more strong warriors in Jiren and Hit, Hearts and his plans to destroy the Omni-King ends up becoming an impossible task.
Gogeta remains undefeated in the Dragon Ball Universe. It makes sense why both Goku and Vegeta don’t like fusing because their opponents end up not being a big enough challenge thereafter.