Infinite health when fighting your friend.
Instead of going to dueling go to practice and choose your characters, then in the fight press start and go to the top bit which says do nothing and press right and it should say guard 1 move it right twice and it should say player controls. Get off the options screen and give your friend the second controller and he will be fighting as well. You will both have infinite health as it is in practice mode.
More tricks, tips and cheats for this game are right here - Dragon Ball Z: Budokai 3 cheats
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