There are a few unlockable secret characters for you to play as.
Bruce Lee – If you have save data from a previous UFC game, you’ll automatically unlock Bruce Lee. If you don’t, he’ll be unlocked once you complete career mode on any difficulty.
Joe Rogan – Play Knockout Mode as George St. Pierre on normal difficulty, with the Sudden Death type activated, and then defeat your opponent with the spinning side body kick.
Bruce Buffer – This one is a bit more complicated than the others. Enter Tournament Mode, name your tournament “Bruce Buffer,” set the type to Strict and the weight class to Middleweight, and then tell it to Auto Fill the fighters. Press start, and Bruce Buffer will replace one of the fighters. Win the tournament to unlock him permanently.