You can beat Emerald with ease using the following materia and abilities:
Phoenix linked with Final Attack
Knights of the Round
Mime
Omnislash
Underwater materia
Also, any form of gravity magic automatically hits Emerald for 9999. So spam that as well. You should have him beat in no time.
Ruby is a different story. I found myself having a harder time with him. You need to go into the battle with two of your characters already dead. In other words, keep Cloud alive lol. You will need to wear a ribbon and have final attack linked with the best revival spell you got *not phoenix like with Emerald cause you will raise all of your allies and he will mess you up hard.*
Hope this helps.







