Dissidia 012[duodecim]: Final Fantasy has an Assist System. You can call other characters from the selectable roster to drop into a battle and help you out.
You do this by building up your Assist Gauge, which you can see in the video above. The Assist Gauge is built up in the traditional fighting game style — by attacking and performing different moves. If you stand idly around, however, the gauge starts to deplete.
You’ll notice the Assist Gauge has two levels. Once the first gauge is filled up, you can press the L and O buttons to call your assist character in for an “Assist Brave” move that lowers your enemy’s brave meter. If you fill the second gauge up as well, you can perform an “Assist HP” move using L + □. This move hits the opponent’s HP meter.