Select the "Load Game" option from the main menu, press and hold Up + B on the second controller and B + Select on the first controller at the same time, then press A on the first controller to enter the selected option. Do not load any games; press B to return back to the title screen and start a new game. From now on, you can finish any battle just by pressing Start on the first controller. This cheat will be saved also to your save slot and you won't need to enter this cheat again, just load a previously saved game.