DBZ WARRIOR

Best answer as chosen by Asker / Ratings
Bardock:
Goku's father can be unlocked two different ways. One way, is to use a memory card with a "Dragonball Z: Budokai 2" save file. The other way: Use Goku's Dragon Universe, and find Raditz's Space Ship (located in the upper mountains,..to the right...somewhat near by the coast). If you find the ship, enter it, and Bardock will become unlocked.

Android 17:
Defeat Android 17 in Piccolo's Dragon Universe.

Android 18:
Complete Krillin's Dragon Universe.

Cell:
Complete Teen Gohan's Dragon Universe. His alternate forms are created through capsules that can be bought at the shop.

Dabura:
Defeat Dabura in Gohan's Dragon Universe.

Cooler's Special:
After you defeat Cooler, another event will be in the same place. BEFORE going to this battle, and AFTER you talk to "Metal" Cooler, search north of his space ship. If you find the right spot, you will unlock the "Metal" version of Cooler (the "Cooler's Space Ship" capsule).

Omega Shenron:
After Broly has been defeated, ignore the red dot and go to West City. After the conversation with Bulma, go and beat Gotenks at the tournament (this will unlock the Gogeta Fusion for Goku). After your battle, a new red dot will appear...Omega Shenron. When you arrive, S.S.4 Vegeta will show up. The two of you will fuse to become, and unlock, S.S.4 Gogeta. If you beat Omega Shenron, he will become unlocked.

NOTE: You will be able to defeat Omega Shenron easily in the transformed state. If you run out of time, and change back into Goku, you are so F**ked!!! Try like hell to use the 100X Big Bang Kamehameha, it will put a serious A**-Whooping on him!!!