Ok. Junction 100 Quakes to Zell's Strength. You can get this magic by refining the Sacred card (red armored Brother) into 100 Dino Bones which you then refine into 20 Quakes each using I believe Time/Space refine ability learned from Diablos. Then, junction Catuar GF to Squall (or whoever has the most HP [you can junction Curaga, Tornado, Life, Full-Life or Ultima to HP to crank it]{also, the Brothers HP+80%}) and Kamikaze Adel. This should do at least 36000. Then have Zell (who should have a Str. of about 255 now) pummel Adel with physical attacks. Also, I believe that you can target one enemy for Duel. (Zell's Limit Break) If so, DO IT! Have your third character use healing items/magic on Rinoa. Adel should fall and you should laugh at how fast this works.

Also, you may want to restart your game since you missed out on Leviathan. I heard that you can get him in Ultimecia's Castle though. So you can wait. (maybe) Also, don't bother with the Deep Sea Research Center for Eden. Draw him from Tiamat in Ulti's Castle. But do go to the Deep Sea Research Center for Bahamut. Go to the Island Closest to Hell and kill things for tons of EXP so you can get to level 100. And tell me that you got Laguna's card from Ellone. It refines into 100 Heroes which makes the final battle a snap.

I am done preaching.