Easy knock:
     Hit  your  opponent until your meter is full and then hit R + L +
KICK  (A  or B) and you will knock him down even when he has his block
on.

Easy training:
     In the training mode go to OFFENSE and hit the blue guy like this:
DOWN + A (twice)
DOWN + B (twice)
I think it's the only way to hit him 30 times. 

Invincible mode:
     Pause the game and press C-Up, C-Up, C-Left, C-Down, C-Right.

Big Gloves:
     Pause the game and press C-Up, C-Down, C-Up, C-Up, C-Down. Repeat
to de-activate.

Big head mode:
     Pause  the  game  and  press  C-Left,  C-Right,  C-Left,  C-Left,
C-Right. Repeat to de-activate.

Restore energy:
     Move  away  from your opponent, hold Z and sweep the Analog-stick
in   circles.  Also  try  tapping  Z  repeatedly  without  moving  the
Analog-stick.

Easy attribute points:
     Select  career mode and intentionally lose every fight so you can
train  to  earn  more attribute points. Once this has been done ten to
fifteen  times,  all  your attribute points should be at the top. This
will  allow  you  to  easily  win your remaining matches, and earn the
championship  after  about  five  fights.  Note: Every time you lose a
fight, you can train again.