The Ultimate is a move within a combo which allows you to finish your opponent off with style. To do and Ultimate, preform a combo on your opponent when their life bar is flashing red, then do the Ultimate in the combo.
There is acctually another type of Ultimate that you can preform. The O-Combo Ultimate. The O-Combo Ultimate allows you to do an Ultimate outside of a combo, which is very convieniant for those of you who are having trouble with the Ultimate. to do it, just do the move when your opponents life bar is flashing red.
The Ultra combo is basically a combo of all of your players moves put into one. The Ultras can range from 20 to about 40 hits. It is a really incredible thing to see. To preform an Ultra, simply do a combo when your opponents life bar is flashing red and while doing the combo, do the Ultra move.
Here is a list of one Ultimate, O-Combo Ultimate and Ultra for each fighter that you'll find in KI Gold.
Note: Most of the moves that you will find here are compatible with Killer Instinct and Killer Instinct 2 as well.