HOM Suicide
Press Down, R1, and L1 during the match to make HOM the robot warrior commit suicide.
Change Camera View
Press L2 + R2 after you pick your characters and while the game is loading.
Change Costume
Hold Up while selecting your character.
Hidden Characters
Complete levels 1, 2, 3, and Udan's Dungeon in Quest mode to obtain the game's hidden characters.
Play as Tori
To get Tori, beat Udan's dungon (almost 30 floors to complete).