V-Hard difficulty setting:
Hold Z and press L(2), A, and B at the difficulty selection screen. 
Alternately, successfully complete the game under the Hard difficulty 
setting. 

S-Hard difficulty setting:
Hold Z and press R, L, A, B at the difficulty selection screen. 
Alternately, successfully complete the game under the V-Hard difficulty 
setting. 

Mewtwo level:
Hold Z and press B, Up, L, B, A, Start, A, Up, R at the trainer selection 
screen. Alternately, successfully complete the game under the S-Hard 
difficulty setting. 

Turbo mode:
Hold Z and press B, A, L(2) at the title screen. The game speed can now be set 
over 50 in marathon mode. Alternately, earn over 10,000 points in the Time 
Zone. 

Secret characters:
Hold Z on controller one and simultaneously press L + R on controllers one 
and two at the two player trainer selection screen. Alternately, successfully 
complete Spa Service. 

Taunts:
Select any two player game mode. Have player one select a character, then 
repeatedly press A.