To inflict more damage with Majin Boo, just throw them into the air and fly directly below them. If you are quick and have enough time, do his Super Ki Blast (powers up a Ki Blast over his head and throws it). If successful your opponent will get hit with all three levels of the Ki Blast, causing an enemy with 400 life to go down to around 220 to 214 of life. This is more than most Desperation attacks.
Hint: Piccolo's arm:
Press Back, Down, Forward and Punch before your opponent hits to see Piccolo's arm disappear then re-grow.
Hint: Vegeta's Desperation Attack:
When Vegeta's power bar is on 80 or less, or when you are playing on training, move Vegeta to your enemy until he can move the opponent across the screen. Then, hold Up. When Vegeta almost lands on the ground, quickly release Up and press Down + Y. Vegeta will pick up his, jump, throw the opponent on the ground, do over 10 Ki Blast, and finish off with his special Blast. Hint: Desperation Attacks: When your character's power bar is flashing red and yellow or when the power bar is on 80 or less, you could use your character's Desperation Attack.
Goku (anywhere): Press Back, Down, Forward, Up + Y.
Vegeta (in front of your enemy): Press Up, Down + Y.
Gotenks (anywhere): Press Forward, Back, Down, Forward + Y.
Gohan (anywhere): Press Forward, Down, Back, Forward + B.
Vegetto (in front of your enemy): Press Down, Back, Down, Forward + Y.
Piccolo (in front of your enemy): Press Forward, Back, Down, Up + Y.
Fat Buu (in front of your enemy): Press Down, Forward + Y + B.
Little Buu (close to your enemy): Press Back, Forward, Down, Up + Y.
Frieza (any where): Press Down, Back + Y + B.
Perfect Cell (anywhere): Press Forward, Back, Forward, Back, Forward + Y
