If your having difficulty beating Emerald Weapon and you can't get the Knights of the Round consider using this method.First equip three gravity materia, one to each character, second if possible equip a mime materia to each character.
Next to one character, equip both the W-Magic materia and quadra magic materia joined to the characters gravity materia. Join an all materia to the other characters materia. Okay. Now when you go into battle all you do is use any level of demi on the Emerald weapon and it automatically does 9999 HP of damage to with every hit but at the end his HP will lower and a couple of hits with a moderately powerful summon spell and he's done for. Voila!

For this you will need Knights Of The Round with at least 3 levels. Phoenix summon with at least 3 levels. Shield with at least 2 levels. Final Attack with any level. About 3 mastered HP and MP pluses (you might need more). 3 Enemy Skills with White Wind learned (to learn White Wind, go to the grassy area of Junon until you fight a big green creature with wings. Manipulate it and have it use White Wind on your party).

You also need MP and HP absorb and the MIME command. Make sure you do NOT have the w-item, w-magic, and w-summon materias. Give everyone HP pluses untill it reaches 9,999 HP. Then do the same with the MP pluses
until it reaches 999. Equip Cloud with the Ultima Weapon and give him the following materia.

Combine the Nights Of The Round with the MP absorb. Give him Phoenix with Final Attack. Give him mime with HP absorb. Make sure that you only eqip these matiera on the Ultima Weapon if their mastered. Give him shield and enemy skill. Give your other party members the other enemy skills. Make sure Cloud has an accessory that will protect him
from Frog and Small.

Before you fight Ruby, get into a battle and have Cloud kill your other party members. Now go after Ruby. Start off by using shield on Cloud. Do NOT have Cloud bring the rest back to life.

Now have Cloud use Knights of the Round and just keep miming it until the Ruby Weapon kills you. When you come back to life, repeat the process until you've won.

NOTE: No matter what, do not use any limit breaks or regular attacks on Ruby. If Cloud becomes a toad, use white wind to heal him.