Complex sentence: Nintendo revealed "Mario & Luigi RPG 3" at a press conference in Japan, where they reveal details of the game relating to the plot and play mechanics, as well as the fact that it would involve extensive use of the touch screen.
Split into simpler sentences: Nintendo revealed "Mario & Luigi RPG 3" at a press conference in Japan. Nintendo of Japan revealed details of the game relating to the plot and game play, as well as the fact that it would involve extensive use of the touch screen.