As Fu observes the planet, he tells a seemingly evil Saiyan that his time will come. After escaping his cell, Future Trunks is confronted by Cooler, who demands a Dragon Ball from him. Meanwhile, Future Trunks is in a prison cell elsewhere on the planet. Fu disappears, and the two Gokus agree to work with each other to escape the planet. Fu deduces that Xeno Goku was trying to use the combined Kamehameha waves to break through the barrier, and explains that the Prison Planet is inescapable unless the group searches for a set of Dragon Balls (one of which is in Xeno Goku's possession) that they can use to escape. The two Gokus engage in a Kamehameha clash, but their blasts cancel each other out.

During the fight, Goku discovers that there is an invisible barrier around the Prison Planet that prevents them from escaping. This Goku, referred to as 'Xeno Goku', sees Fu and assumes that the trio are working for him he immediately transforms into Super Saiyan 4 and attacks Goku, who reacts by transforming into Super Saiyan Blue. The trio arrive on the planet and meet an alternate version of Goku, who is revealed to be part of a group called the Time Patrol. A mysterious figure emerges, introducing himself as Fu he tells Goku, Vegeta and Mai that Future Trunks is trapped on a world called the 'Prison Planet', a planet where warriors from alternate timelines and dimensions fight as part of an experiment conducted by Fu. Goku and Vegeta's training with Whis and Beerus is interrupted by the arrival of Future Mai, who tells them that Future Trunks has been captured. Goku! A Transcendent Battle Begins on the Prison Planet!' ( 悟ご空くうvs 悟ご空くう！監かん獄ごく惑わく星せいで超ちょう絶ぜつバトル開かい幕まく！, Gokū vs Gokū! Kangoku Wakusei de Chōzetsu Batoru Kaimaku! ) Episode listing Universe Mission Prison Planet Saga

Dragon ball super heroes episode 15