High Summoner Yuna! Know true Ronso anger!
The difficulty of the battle is determined by the player's responses to the Ronso's concerns during Chapters 1 and 2. If the "right" answers are given, Garik will be weaker than normal and only have a single Ronso Youth. If the player gave them the "wrong" answers, Garik will be stronger and have two Ronso Youths aiding him.
When Garik is in his stronger form, he will use Mighty Guard, and the Ronso Youth will drain the party's MP. The Gun Mage can only learn Mighty Guard from Garik during this battle if he is not weakened, and he must be confused to cast it on one of the girls.
If Garik is weaker, he won't use Mighty Guard, and the Youths won't drain the party's MP. Garik's Defense is also weaker in this form.
The player should Dispel Mighty Guard's effects, and hit him with the party's strongest attacks. A good strategy is to concentrate on one enemy at a time, usually starting with the Ronso Youth. After both cronies are taken care of, the party can pummel Garik. A high-level Berserker is helpful.