1. Ancient Wrath
This rumor centres on the fact Aeris must be revived. Once Aeris comes back, visit her house in Midgar and you'll find Elmyra waiting inside. She'll approach Aeris and give her the Ancient Wrath, Aeris' Ultimate Weapon. Supposingly this weapon was found with Ifalna when Elmyra rescued Aeris.
Fill all the materia slots of Cloud's Ultima Weapon with mastered Knights of the Round materia, and it will transform into the fabled sword 'Excalibur'. According to Biske Gallant, the stats for this weapon are 110 Power, 200% Accuracy, four materia slots, and normal materia growth.
3. Jenova Claw
Have Tifa in your party when you fight the monster Jenova*DEATH. Have all of your party members beside Tifa killed, and win the battle. Victory shall reveal Tifa's secret weapon, Jenova Claw.
4. Jupiter Blade
With the Shinra submarine, explore the underwater area and you'll find a secret, sunken pirate frigate. Board it, and you'll find a secret weapon, Cloud's Jupiter Blade.
Win over 10,000 points at the roller coaster ride in the Gold Saucer and instead of just winning a replica, you'll win the proper Masamune Blade - Sephiroth's weapon.
There's supposedly another way, by Eecetera@aol.com. Get 5 pieces of Mythril from the sleeping man in the cave, give it to the weapon seller, and he will give you a secret weapon for Cloud, the Masamune.
6. Cloud's Level 5 Limit
Eecetera@aol.com professes a way of using Cloud's fifth level limit break. According to him, everyone must be at level 99. Ensure Cloud has all master summon in his Ultimate Weapon and all master masic in his equipped Wizard Bracelet. Cloud must have his Level 4 Limit equipped, and have killed 129 monsters with Omnislash. By doing the above, when you fight Sephiroth, instead of using Omnislash, Cloud will use the Level 5 limit called Hyper Cut.
7. Zack's Limits
Apparently the following is a rumored list of the Limits for Zack. This was contributed by Eecetera@aol.com:
1. Omnislash / Spiral Crush
2. Super Cut / Mega Speed
3. Gouging Twist / Flying Combo
4. Super Omnislash