Enter Mr. Skitz as your first name in create a champ mode to have full stats.
Enter NEWVIEW as your first name in create a champ mode to unlock all arenas.
Win a career mode fight at the Staples Center or Madison Square Garden to unlock it.
Fight as Ko Rey Mo:
Beat Ko Rey Mo in the light heavyweight division to unlock him.
The Burger King as your trainer:
Beat the Burger King event in career mode, then when selecting your trainer, press Down until Burger King is selected.
Win matches in ESPN classic fights mode or career mode to unlock the fighting styles used by your opponents
Easy career wins:
Set Illegal Blows to 'off'. Get the illegal blow 'Elbow Shot' from the store, start a fight and use it as a counter. Ouch!
Thanks to Revolution Reader tehbaddstman!