This only works with Liu Kang. When you're given the chance to do your fatality, get as far away as you can, and then do the motion. If done right, Liu will cartwheel, but not throw an uppercut. The opponent will still stand there and waver, even when the fight officially ends. However, since you did the cartwheel, the game has registered you as doing the fatality, meaning you'll get the bonus as if you actually did so. You can also throw fireballs after doing this trick for extra points.