I fight the third Elemental Archfiend Barbariccia. Yang,Cecil, and Cid should attack while Kain jumps. Barb can also turn into a tornado but Kain's jump attack will make her stop that but be careful because her Ray attack can cause petrification after a while so have Rosa cast Esuna on whoever got hit by that, and her other attack is Tornado where she makes a Character's HP go to single digits so have Rosa cast Cura on that character. You can either have Rosa use Aim or Pray whenever shes not on healing duty.