box as a bear=at the main menu press right, square ,right, triangle, right, circle, right, x.if you entered it correctly you will hear some sound then select any boxer to play as the bear. 
Submitted by Toboggan

PSI RULES!?

For 100% speed, streangth and stamina go to career mode, create a player called PSIRULES. exit carrer mode by pressing start and go to yes. Reenter career mode, select the player PSIRULES and he will have 100% everything and other greatfeatures like lose hardly any life when the opponent hits you.
Submitted by Michael Mckenzie

taunt opponent

in a match press R1 R2 x. 
Submitted by Toboggan

big heads

at main menu press left, circle, left, triangle, left, square, left, x.