Final Flight is the Supermove of Superman, which is performed by pressing
once you've filled the meter to four bars. You fill your meter quicker by performing Super Moves, which can be viewed in the pause menu.
To earn this trophy, you must finish Green Lantern with this move. So go into Very Easy Single Match or, if you have two controllers, Versus. Choose Superman, then pick Green Lantern as your opponent. Then, take down Lantern until he has around 25% health, and with a full meter, perform the move and you should win the match with this move.