Ruby Weapon can be found in the desert around the gold saucer. You should fight this guy first, because he’s a lot easier than Emerald. Make sure you save before the battle! The first this you should do is cast Big Guard with the character with the Enemy Skill materia. Then you hope that Cloud isn’t the one who Ruby whirlsands away. If he is, just reset the game and try again until he’s the one left. Then start your attack by casting Bahamut ZERO twice. BZ will be cast five times, eight if Quadra Magic is at level two or higher. You won’t probably do any serious damage to Ruby, but that’s not the point. The point is to get him to stick his tentacles in the ground.
At this time you MUST have at least 250 MP left, if not, use a Turbo Ether or Elixir to boost you up. Now cast KOR twice, once at the tentacles and once at Ruby himself. If KOR is at level one, it will only be cast once, on the tentacles, but that’s okay. Since you’ve got a lot of magic power, thanks to Magic Plus, the tentacles will probably be destroyed, and because you’ve got KOR linked with HP Absorb, you’ll be healed to full health too.
After this, just use Mimic every turn until Ruby goes belly up. Every turn, you’ll cast KOR twice for zero MP, and get healed to full health after each KOR. You don’t have to worry too much about Ruby’s counterattacks, because thanks to the Mystile armor, he’ll miss most of the time, and then you’ll get healed by KOR. Just keep mimicing, and you’ll kill Ruby in no time.
Emerald Weapon swims around in the sea just outside Junon. Use the submarine to find him. Start off with the character with BZ and KOR cast first a BZ and then a KOR. Then have Cloud use Mimic. The first character will cast BZ four times, and KOR once, and get healed by KOR. Then Cloud will do the same thing. Don’t do anything with the third character, just wait for it to be Cloud’s turn again, and use Mimic again, then repeat the procedure. Just skip everyone except Cloud, and have Cloud use Mimic.
Don’t worry about the other characters getting killed, just keep mimicing. Sooner or later, Emerald will use Aire Tam Storm on you, and you’ll die. Just before you die, however, you’ll use Final Attack and cast Phoenix. Not only will you do damage to Emerald, but everyone will be brought back to life with full health. Now use the second character to cast KOR twice, then mimic with Cloud. Continue to mimic with Cloud, and Emerald should be dead in a few turns.
This is by far the most annoying weapon. The first time you fight him, all you have to do is survive his attacks and attack back for a couple of rounds. The next time you fight him, I forget but here’s how to beat him. When you can, take the Highwind over Lake Junon (waterfall, deep pool, near Junon). If you see a large black monster over it, that’s Ultima Weapon. If not, try again later.
When you fight him the first time, any attacks that are long range will hit him. When he’s taken enough damage, he will fly away. Now, you have to chase him in the Highwind until he stops moving. Then you’ll have to fight him again. When he makes his final stop at Cosmo Canyon, beat him and he will explode in the canyon creating passage for the ancient forest. You can get the Ultima Weapon after you beat him.
This is by far the easiest weapon to beat. He is the one that comes out of the water and starts advancing toward Midgar. Basically, all you have to do is to pummel him until he’s dead by attacking with summons and maybe magic, I forget. Remember that he is invulnerable to physical attacks until after he does Diamond Flash. Anyway, cure yourself when you’re low on HP and that’s how to beat Weapon. You can also steal a Rising Sun from him.