First you will need 1 Master Comet materia, 1 Master Quadra Magic materia and 1 Hi-Potion. Before you fight with Ruby, kill the 2 members of your party then equip Comet linked w/ Quadra Magic in the weapon/armor of the remaining member and make your HP go to 7677. After you've done the following fight Ruby weapon. At the start of the game Ruby will stick it's claws to the ground, use the Hi-Potion and you will have the All Lucky Sevens and will attack Ruby 62 times w/ 7777 damage, after the 62 strikes Ruby will retract it's claws, use Comet 2 w/ Quadra Magic on Ruby then it will stick its claws again after that use Comet 2 w/ Quadra Magic on it's claws and it will retract it again, continue attacking it and it's claws alternately until you defeat ruby. Note: If done correctly you can even beat him without taking any single damage.