DBZ WARRIOR

Best answer as chosen by Asker / Ratings
Use Goku's Dragon Universe for AT LEAST the second time. Now, reach the Majin Buu Saga. The trick to unlocking Uub is this: you have to beat Kid Buu with the "Super" Spirit Bomb. Here's what you do: Before the battle with Kid Buu, you have to adjust you skill tray. YOU MUST HAVE THESE THREE IN ORDER FOR IT TO WORK: Kaioken, Super Saiyan, and Spirit Bomb (As for the rest, I used: Z-Sword,Concentration, Saiyan Spirit, and Kamehameha). DO NOT POWER-UP HIGHER THAN KAIOKEN DURING THE BATTLE OR YOU WILL NOT BE ABLE TO DO THE "SUPER" PART OF THE SPIRIT BOMB!!! Wail until Kid Buu's energy is in the "yellow", and then do the spirit bomb. YOU MUST WIN THE "POWER STRUGGLE" IN ORDER TO DO THE "SUPER" SPIRIT BOMB!!! If all is done correctly, Goku will transform into a Super Saiyan and finish off Kid Buu. After this battle, go to the red dot. If you defeat Uub at the World Martial Arts Tournament, he will become unlocked.

NOTE: BEFORE you go to the tournament, head to the islands that are East/right of the tournament. Find the one with the ???, which will trigger a very "Odd" scene. After that scene, the S.S.4 capsule (for Goku ONLY) will be unlocked.