Barbarossa is fond of offensives, often using Brave to attack with the defense-lowering Shell Split followed by the increased power of Double Damage. He will also attack with Defang, which will reduce the attack power of its target.
Strategy[]
Barbarossa is not all that complicated of a boss fight. A high enough level Knight and a couple of Black Mages with powerful lightning attacks should bring him down in a pinch. Knights with high defense and defense increasing abilities can easily withstand his attacks as well as protect other party members. Barbarossa's Defang move will reduce the attack power of the target, but since it's wise to stick with magic attacks considering his weakness, this doesn't mean all that much.