In addition to the 12 characters available to you at the start of the game, you can also earn 5 more characters to use in any mode of play, by accquiring 7 Dragon Balls in either Z Survivor or Original mode.
Once you've collected 7 Dragon Balls, select Shenron from the main menu. If you've made at least two other wishes, you may select Enhanced Wishes. Once there, here's how to unlock more characters:
King Piccolo: Wish for him from Shenron in the Enhanced set of Wishes. Majin Vegeta: Wish him from Shenron in the Enhanced set of Wishes. Videl: Once you've made over over 5 wishes in total, you may wish for her from Shenron in the Enhanced set of Wishes. Mecha Frieza: Once you've made over 10 wishes from Shenron, you may choose him in the Enhanced set of Wishes. Ultimate Gohan: Wish him from Shenron in the Enhanced set of Wishes.
