Alright, I found a glitch in ToS, to make yourself completely invincible. To do it, follow the instructions below:
Go into a battle with low HP, and are able to use a unison attack IMMEDIATELY
Now, just as you get hit and loose your remaining HP, quickly unleash your unison attack. Your timing must be perfect.
Now, the character who unleashed the U. Attack will continue the attack with 0 HP, and when the unison attack ends, your character will continue to fight, with 0 HP. You will still take damage from monsters, they just cannot kill you. I dunno if they fixed this for the PS2 version, but thanks to it, I was able to destroy Shadow (The summon spirit) single handedly with Lloyd (To bad Kratos is gone at that time). Also, if you have a healer on your team, MAKE SURE IT DOES NOT HEAL!!! The healer will bring back your HP, and you'll have to do it all over again. Make sure you have characters alive who are not in your attack team, because after the battle, your fighting team will die. If your against a boss you think is invincible, think again!