To guard hold a+b...
Edit:
Here are the game moves
A - weak attack
B - strong attack
(hold)A+B - block
(close range) A+B - character special attack
L - swap character
(hold)R - power up
tap direction twice - dash
direction + R - power dash
R+B - weak enery blast
R+A - strong enery blast
R+A(hold) - even stronger enery blast
R+A+B - character special enery blast
note that a char can have more then 1 special energy blast, try facing the opponent in different directions, and some moves can(only) be done with 100%
Note that this is lifted from a post on Gamefaqs so I'm not taking credit for the moves list...