BOSS BATTLE: Kary
You're in luck. This isn't as bad as the Lich rematch was. She has more Health than he did, but her magic is not as deadly. You do need to watch out for Fire 3 and Blind. Casting Anti-Fire will help if your White Wizard has it. Knights, Ninjas, and Masters should be attacking. Have a Black Wizard or Red Wizard casting Haste and Temper on your main fighter. Heal as needed. You should be fine as long as you entered the fight at full Health. It's really not as bad as it may sound. Kary was arguably the toughest in the original elemental fiend battles, she's probably the easiest in the rematches oddly enough.