Ruby Weapon
To find Ruby Weapon search the sand prison surrounding the Gold Saucer. He
will attack you immediately so be prepared!
The following are all of the battle preperations. Make sure you have a few Mastered Knights of Round materias or a Master Summon materia equiped on the same person who has W-Summon, preferrably Cloud, but its up to you. Give a different person the W-Item materia and another person an Enemy Skill materia with Angel Whisper, White Wind and Big Guard. Make sure everyone is wearing an armor with a very high magic evasion %, like the Mystile or Aegis Armlet. If you run out then equip them with Ziedrichs or Wizard Bracelets, which have high magic defenses. Because of Emerald,s high defense and magic defense, Limit Breaks and most magic spells are rendered useless. If you feel Limit Breaks are a necessity, then make sure the strenght stats of your characters are very high. Being at level 99 will definitely help, too. Megalixers and Hero drinks should be abundant in your inventory as well. Equipping Ribbons on each of your characters helps, a lot. Ultimate weapons shouldn't be equipped - they won't make you much stronger, they'll just cause your materia to gain no AP. The following is very important: make sure you kill 2 people before battle, the ones that don't have Master Summon and W-Summon. This will prevent Ruby Weapon from tossing characters out of battle and will also force him to put his claws in the ground, thus rendering him no longer invincible. The rest of the equipment is up to you.
If you didn't follow my instructions, particularly the last one, you're as good as dead. Now, use W-Summon with the character that is alive to summon Phoenix and then Knight of Round in that order. Phoenix will revive your characters and KOR will do a ton of damage as well as cause Ruby to counterattack with Ultima. Its very important that you never use 2 KORs in one turn because you risk death. The Mystile and Aegis Armlet armor should make about half of the Ultima castings miss. Have one character W-Item Megalixers and Hero Drinks and the other use Big Guard, White Wind and Angel Whisper as needed. Have the character with W-Summon cast KOR and then Phoenix or KOR and then Bahamut ZERO, it depends on your current situation. Also, make sure your highest Hero Drink priority is the summoner. Ruby Weapon should die shortly.
After his much anticipated death,
Ruby will leave you a Desert Rose, which you can take to the old man on the
second floor of a house in Calm. In exchange he will give you a Gold Chocobo.
Goldy appears in your stables automatically. This is your only way around
breeding for getting all of those special materias!