here are some ways you can unlock characters for the game. (from gamespot.com)
Fuses To Unlock (Purple Potora only) unlockable characters
Perfect Cell(Perfect Form) Super Saiyan Goku + Cell Perfect Form
Vegeta (Scouter) Vegeta + Scouter
Super Saiyan Super Trunks Super Saiyan + Super Saiyan Trunks
Super Saiyan 3 Gotenks Super Saiyan + Super Saiyan Gotenks
Super Vegito Super Saiyan + Vegito
Broly Super Saiyan + Broly
Frieza Final Form(Full Power) Frieza Final Form + Super Transformation
Mecha Frieza Frieza Final Form(Full Power) + Reconstruction Surgery
Super 17 Android 17 + Android 17
Great Saiyaman Gohan + Transforming Hero set
Ultimate Gohan Super Saiyan 2 Gohan + Elder Sumpreme kai
Majin Buu(Gotenks Absorbed) Super Saiyan 3 Gotenks + Absorption
Majin Buu(Pure Evil) Majin Buu(Good) + Wicked Person's Bullet
Super Saiyan Gogeta Goku's Fusion + Vegeta's Fusion
Bojack (Post Transformation) Galactic Warriors + Seal Release
Cooler Final Form Frieza's Older Brother + Super Transformation
Janemba Psyche Orge + Peoples Maliciousness
Majin Vegeta Super Saiyan 2 Vegeta + Babidi
Super Saiyan 4 Gogeta SS4 Goku's fusion + SS4 Vegeta's fusion
Bardock Kakarot + Hatred of Saiyans
Majin Buu(Ultimate Gohan Absorbed) Ultimate Gohan + Absorption
Baby Vegeta Tuffles + Artificial Bruits Waves
Characters
Kid Goku Collect the 7 Dragonballs in Z Battle Gate
Oozaru Collect the 7 Dragonballs in Z Battle Gate
Tai Pai Pai Collect the 7 Dragonballs in Z Battle Gate
Master Roshi Collect the 7 Dragonballs in Z Battle Gate
Super Saiyan Goku Beat Frieza with him in Z Battle Gate
Super Saiyan 2 Goku Beat Perfect Cell in Z Battle Gate
Super Saiyan 3 Goku Beat Majin Buu with him in Z Battle Gate
Super Saiyan 4 Goku Beat Super Android 17 with him in Z Battle Gate
Super Saiyan Vegeta Beat Android 18 with him in Z Battle Gate
Ultra Super Saiyan Vegeta (Super Vegeta) Ussj Vegeta vs Kid Buu (Let timer run out)
Raditz Beat him with Piccolo in Z Battle Gate
Nappa Beat him with Goku in Z Battle Gate
Dodoria Beat him with Vegeta in Z Battle Gate
Guldo Beat him with Chaozu in Z Battle Gate
Recoome Beat him with Goku in Z Battle Gate
Burter Beat him with Goku in Z Battle Gate
Ginyu Beat him with Goku in Z Battle Gate
Frieza 2nd Form Beat him with Kid Gohan in Z Battle Gate
Frieza 3rd Beat him with Vegeta in Z Battle Gate
Frieza Final Form Beat him with Vegeta in Z Battle Gate
Super Saiyan Future Trunks Beat Mecha Frieza with him in Z Battle Gate
Android 16 Beat Cell with him in Z Battle Gate
Android 17 Beat him with Piccolo in Z Battle Gate
Android 18 Beat her with Ssj Vegeta in Z Battle Gate
Android 19 Beat him with Ssj Vegeta in Z Battle Gate
Android 20 (Dr. Gero) Beat him with Piccolo in Z Battle Gate
Perfect Cell Beat him with Ssj2 Gohan in Z Battle Gate
Hercule Beat Perfect Cell with him in Z Battle Gate
Videl Hercule vs Kid Buu (Let timer run out)
Goten Beat Adult Gohan with him in Z Battle Gate
Super Saiyan Goten Beat him with Kid Trunks in Z Battle Gate
Kid Trunks Beat Vegeta with him in Z Battle Gate
Super Saiyan Kid Trunks Beat Hercule with Kid Trunks in Z Battle Gate
Gotenks Beat Super Buu with Ssj Gotenks in Z Battle Gate
Super Saiyan Gotenks Beat Super Buu with Ssj3 Gotenks in Z Battle Gate
Dabura Beat him with Gohan in Z Battle Gate
Majin Buu Beat Super Buu Gohan with Vegeto in Z Battle Gate
Vegito Majin Buu vs Kid Buu (Let timer run out)
Oozaru Vegeta Collect the 7 Dragonballs in Z Battle Gate
Kid Buu Beat him with Goku in Z Battle Gate
Sorry for going off topic but here is how high you can fly in the game. http://www.gamedaily.com/general/animegamehub/screenshots.asp?id=4275&s=1&page=30. It is a little slow, so be patient.
PS Gamers Network - My new website, please contribute. Includes Wii and 360 Forums as well. http://z15.invisionfree.com/PS_Gamers_Network