In Dragon Ball: Raging Blast 2 for the PS3 and Xbox 360, there is a nice sized list of characters you can unlock by doing certain things in the game. Most of them are done by beating boss missions in Galaxy Mode with certain characters, but one is unlocked a little differently.
There may be multiple ways to unlock some characters, so please only leave corrections in the comments if you know that one of these does not work.
Android 13 – Beat Dr. Gero’s boss mission in Galaxy Mode
Android 14 – Beat Android #13’s boss mission in Galaxy Mode
Android 15 – Beat Android #14’s boss mission in Galaxy Mode
Bardock – Beat Saibamen’s boss mission in Galaxy Mode
Bojack – Beat Zangya’s boss mission in Galaxy Mode
Broly (SSJ3) – Beat Broly’s boss mission in Galaxy Mode
Cooler – Beat Frieza’s boss mission in Galaxy Mode
Demon King Dabura – Beat Cell’s or Goten’s boss mission in Galaxy Mode
Doore – Beat Neizu’s boss mission in Galaxy Mode
Gogeta – Beat Future Gohan’s boss mission in Galaxy Mode
Gogeta (Super) – Beat Vegito’s boss mission in Galaxy Mode
Gohan (Adolescent ) – Beat Teen Gohan’s boss mission in Galaxy Mode
Gohan (Future) – Beat Mystic Gohan’s or Ultimate Gohan’s boss mission in Galaxy Mode
Gohan (Teen) – Beat Kid Gohan’s boss mission in Galaxy Mode
Gohan (Ultimate) – Beat Adolescent Gohan’s boss mission in Galaxy Mode
Gotenks – Beat Super Gogeta’s boss mission in Galaxy Mode
Hatchiyack – Watch the “Dragon Ball Z – The Plan To Eradicate The Super Saiyan!” movie in game
Janemba – Beat Pikkon’s boss mission in Galaxy Mode
Kid Buu – Beat Krillin’s boss mission in Galaxy Mode
Mecha-Frieza – Beat Meta-Cooler’s boss mission in Galaxy Mode
Meta-Cooler – Beat Cooler’s boss mission in Galaxy Mode
Neizu – Beat Burter’s boss mission in Galaxy Mode
Pikkon – Beat Piccolo’s boss mission in Galaxy Mode
Salza – Beat Doore’s boss mission in Galaxy Mode
Tarble – Beat Battle Zone 2 with Vegeta
Trunks (Sword) – Beat Trunks’ Fighting Teen boss mission in Galaxy Mode
Turles – Beat Raditz’s boss mission in Galaxy Mode
Vegeta (Majin) – Beat Vegeta’s (Scouter) boss mission in Galaxy Mode
Vegeta (Scouter) – Beat Goku’s boss mission in Galaxy Mode
Vegeta (SS3) – Beat Majin Vegeta’s boss mission in Galaxy Mode
Vegeta (SSJ3) – Beat SSJ3 Broly’s boss mission in Galaxy Mode