Instructions
Max out all of your characters' health and magic powers before starting the battle. Use potions to get up to full power.
Select a character that you perform well with in the game. Try to make the character a shorter character: someone as tall as Kid Buu. A taller character will kick right over his head, giving you a major disadvantage early in the fight.
Defeat all the characters in Kid Buu's level to earn three more free turns. These will act as a great advantage in the fight, enabling you to attack Kid Buu three times without him attacking back
Equip the vaccine and the Death Move. Block his attacks regularly and wait for him to pause. After he pauses, use your special attack to stun him. If you cannot hit him with your special attack, try hitting him with kicks and punches to stun him. Use the Death Move on him while he is stunned. This will drain a lot of his power.
Keep blocking and using your special attacks and death move until he is defeated. If he hits you, use your vaccine to save yourself from death.