For beating Emerald WEAPON, I reccomend being AT LEAST level 70. Have 3 mimes, AT LEAST 2 final attacks, knights level 2, W-summon, Phoenix at least level 3, 2 mastered revives, 3 mastered hp plus, and a mastered hp absorb. Make sure that none of your party members have more than 9 materia, or Emerald will use Aire Tam to kill them instantly. Start off by using knights paired with the hp absorb. That character should also have W-summon equipped. Then, simply keep using mimes with each character. If you happen to get unlucky, Emerald will kill a character. If this happens early on in the battle, your screwed, because you can't mime knights anymore. The battle should take roughly 25 minutes...as it took me 25 minutes. Make sure you have the underwater materia equipped. If you havent beaten Ruby WEAPON yet, try not to use Ultima Weapon, as you won't get the wonderful 50,000 AP. (if you like this walkthrough, tell me, and I will put one up for Ruby)