Cheer and defence +20 is important, becuase if you cheer 5 times, NONE of Penance's attacks can kill you with one hit. This means that 3 stars will last indefinately, sinse none of your characters will die.

Also, Auto potion with X-Potions is better than using Megaelixers, because it doesn't waste even a fraction of a turn, like using quick pockets would.

With the stratagy that I described it is IMPOSSILBE (seriously, not just a boast) to lose.