Buy Antidotes and Softs to customize Stone and Poison Ward onto your armor (which can also be bought from Rin). Cast Haste on your characters, and Slow on Evrae. After you knock off half of his HP, he'll caste Haste on himself. DON'T attempt to recast Slow on him, as he'll just be able to cast Haste again and skip the rest of your turns (so he gets to cast Haste and attack). Using Cid's missiles helps a bit, but they don't do all that much damage. Use Al-Bhed Potions when necessary, and Evrae shouldn't be too much of a problem.