This is a glitch that involves the use of Stahn's Phoenix Sacred Skill. Get Stahn poisoned and have his HP reach to the point where the poison damage in battle would kill him ( Choose to go to 1 to be on the safe side). As soon as you get into battle use Phoenix. Stahn should be killed in the middle of Phoenix's attack animation and then revive him with a Life Bottle. The fire attack animation of Phoenix should still be visible and Stahn will be completely invincible. You also have full control of Stahn just as if you are using him normally. So in turn, while this glitch is in effect you are completely unstoppable and nothing will be able to hurt you (Not even enemy spells can hurt you!). I show off the final 3 bosses of the game and how they can't even stop this amazing glitch!
seeGAMEPLAY