First, Gohan and Future Trunks put their hands above their heads and charge their Masenko attacks. Then, they fire them simultaneously so they merge into a large Masenko blast at the opponent, inflicting a huge amount of damage.
Gohan and Future Trunks use this attack during the battle against the Legendary Super Saiyan Broly in the movie Dragon Ball Z: Broly - The Legendary Super Saiyan. When Broly dodges Goku and Piccolo's attacks, Gohan and Future Trunks appear and fire the Combined Masenko against Broly. However, it has little effect against the Legendary Super Saiyan, aside from destroying the stone tower he stood on.
Appearances in games
Gohan and Future Trunks uses this technique against Giant Form Hatchiyack in the Playdia game Dragon Ball Z Gaiden: Shin Saiyajin Zetsumetsu Keikaku - Uchū-Hen.