Successfully complete the game in Street mode under the hard difficult setting with all eight Mobile Suits and complete Time Attack A mode in five minutes or less to unlock Big-Zam in Versus, Time Attack, and Survival modes. The easiest way to get the Big-Zam is to play Time Attack A with the Dark Gundam and constantly use the Double Hand Beam (Forward, Down, Back, Punch). It gives the enemy mega damage and it is unblockable. It is possible to complete Time Attack A in three minutes with this trick.