When fighting Justiss, you must throw him into the flames that come out of the pipes on the wall. Just trying to beat him up will not work, as he will not lose any health. Punch and kick him a few times, then throw him towards the flame valves. Throw him beside a flame valve that is lit. Punch and kick him to keep him close to the wall until the flames come on, then run the other way as fast as possible. Keep punching and kicking him to build up your special while you are trying to put and keep him against the wall. Do not perform any specials just yet. Once it goes into the next intermission sequence, the flames get turned off and he starts losing health when you hit him. When the intermission sequence is playing, he calls in some backup (about three or four men). Ignore them. When the intermission sequence is done, run directly towards Justiss and do a Heavy special (press Y, Y, X; or Y, Y, A; or Y, Y, B). This will bring his health down a lot. If you only end up doing a Brutal and use two special bars, beat down the backup. Fatal them so that you get health from them, then do another big attack on Justiss. At this point, he should be into the "Y" Fatal stage. Run up and press Y, then just protect yourself from the backup until the intermission sequence begins. You will then be King Pin.
