equip knogol with the legend casque and a phantom shield. he'll be almost invincible to Foust's magic, and his physical attacks do almost 3000 damage if u have fully upgraded his bone crusher. then its just a matter of healing the other 2 people near the end

foust is the most poswerful in the game you just have to level up alot before you fight him and than have dart( you have to have him) equipt with the thearpy ring to heal every turn, shana or miranda depending on what point you are at in the game and have her equipt with amulet or what ever it is that doubles your maxium magic and whatever your other strongest character is i went with albert and had him equipt with the speed ring or what ever it is called the accessory that makes the character faster. Have items to revive, heal like healing rain, and to give you more magic and just attack away and when your health gets low eithr use the healing rain or use the white dragon attack since it will take out a good amount of his health and heal you and you just have to keep doing this.