To get Uub,...and YES: YOU CAN GET HIM, just follow these simple instructions:
Before you battle Kid Buu, reconfigure your skill tray. This is what I used:
2. Super Saiyan
4. Spirit Bomb
5. Z Sword
6. Saiyan Spirit
Contrary to popular belief, you DO NOT NEED Super Saiyan 2.
Make sure that you DO NOT transform higher than Kaioken during your battle with Kid Buu. When his energy is in the "yellow", do the Spirit Bomb. You need to win the power struggle in order to create the "Super" part of the attack.
To do this: When the power gauge is close to being full, press X ( ANY ONE OF THE FOUR WILL DO, your choice). You will have three chances to get it as full as possible. There is a "MAX" reading at the very end of the Gauge (when it has become completely full, but your timing needs to be perfect). IF YOU DO NOT WIN THE POWER STRUGGLE, YOU WILL NOT BE ABLE TO GET UUB!!!!!
If you win the power struggle, Goku will become a Super Saiyan and defeat Kid buu with the "Super" Spirit Bomb (just as he did in the series). You will notice that the story line will continue, and a new red dot will appear on the map at the World Martial Arts Tournament. Go to the tournament: if you defeat Uub, he will become unlocked.
On a side note...Before you go to the Tournament, head to the islands to the East of the Tournament itself. You should find a ???, where an interesting scene will occur. More Importantly, it will unlock the S.S.4 Capsule for Goku!!!!!
Death is but a door, Time is just a window,...I'll be Back!!!!!