Android #16.
Complete the "Aim For Perfect Form" episode to unlock Android #16.


Android #18.
After you finish story mode, re-enter it. Go to the Android Saga and find the new episode Super Saiyan Vegeta. Enter this episode and you will end up fighting Android #18. Once you defeat her, you will get a new skill that states that you can now use Android #18 anytime.


Cell, Android #17, and Teen Gohan.
Play through "The Androids Saga" at any level to unlock Cell, Android #17, and Teen Gohan.


Dodoria.
Defeat Recoome with Vegeta.


Freiza, Ginyu, and Recoome.
Play through "The Namek Saga" at any level to unlock Freiza, Ginyu, and Recoome.


Mr. Satan (Hercule)
Win a World Match Tournament at the "Adept" level to unlock Mr. Satan (Hercule).


Radditz, Vegeta, and Nappa.
Play through "The Saiyan Saga" at any level to unlock Radditz, Vegeta, and Nappa.


Saiyaman (Gohan's alter ego)
Win a World Match Tournament at the "Advanced" level to unlock Saiyaman (Gohan's alter ego).


Super Saiyan ability (Goku only)
Play through "The Namek Saga" at any level to unlock Super Saiyan ability (Goku only).


Super Saiyan ability (Vegeta only).
Play through "The Androids Saga" at any level to unlock Super Saiyan ability (Vegeta only).


Super Saiyan and Super Saiyan 2 abilities (Teen Gohan only)
Play through "The Androids Saga" at any level to unlock Super Saiyan and Super Saiyan 2 abilities (Teen Gohan only).


Super Vegeta.
Complete the "Vegeta's Confidence" episode to unlock Super Vegeta.


Trunks.
Complete the "Perfect Form Cell Complete" episode to unlock Trunks.


Yamcha.
Complete the "Aim For Perfect Form" episode to unlock Yamcha.


Zarbon.
Complete the "Vegeta's Attack" episode to unlock Zarbon.