TIPS FOR FIGHTING EVRAE
The worm on the airship the first time your on it, also you can hire Wakka, brother and a few other players for blitzball now. GET BROTHER!!!
Buy weapons from Rin with hp + 10% and customize with poison wards for everyone, he sells antidotes too, which is needed for poison ward.
This is what I did. Of course your methods may vary this is only a suggestion.
I pulled back first off, in order to avoid his poison attack, then cast haste on Tidus, Lulu, and Wakka, cast blizzara, dark buster and just have Tidus use cheer on his turns, this may also be a good time to cast haste on any other strong characters. I think you can use slow on him too before he�s down to apprx. 12000 hp.
Continue this until he has about 15000 hp left and move in, now you'll have to deal with poison and stone, but you'll avoid his swooping attack, as soon as your closer to him have Tidus use Delay Attack as much as possible.
That worm will cast haste on itself when it�s down to about 12000 hp, even when it's not his turn so don't worry about getting rid of it, if you do manage to get rid of it he will automatically cast haste again, so don�t waste a precious turn.
Just keep using delay attack. After you�ve moved in bring in your strongest hitters and attack with all you�ve got. Keep hitting it with Delay Attack and Dark Buster.
I used al bhed postion if one person turned yellow, stoned, or poisoned. This helps cure damage and takes care of stone and poison.