In order to do so, you need to lock on an enemy, cycle among different parts, and focus your attacks on it. (segmentnext.com)
The third and most powerful level of focus attack automatically triggers after a second or so of holding the buttons down. (thatvideogameblog.com)
Four brand new fighters would get tossed into the mix as well, and a versatile focus attack would evolve the fighting with new combos, counters, and techniques. (thatvideogameblog.com)