Acquiring the Keystone
Make your way back to the Gold Saucer by heading to North Corel and taking the lift at the Ropeway Station. You’ll have to buy another 3000 Gil ticket if you didn’t already buy the lifetime pass (if you sold off an master-level All Materia, you should have more than enough money to buy one now) but 3000 Gil shouldn’t be a considerable sum anymore, especially when you can earn that much in one battle near Mideel (the south-eastern islands). Once you’re back inside head to the Battle Square, where there’s considerably less death and misery now than there was last time you were here.
Head upstairs to reach the registration area of the Battle Square, which now merits some description; in the Battle Square you can spend GP to compete in the arena. Win battles and overcome random handicaps after each match to earn Battle Points, which you can redeem at the computer terminal in the south-eastern corner of the registration area. There are some legitimately awesome prizes you can win, including potent accessories, unique Materia, and Cloud’s ultimate Limit Break. With the proper gear, preparation, a bit of luck, and whole lot of patience, you can win most of these prizes now, but it’ll be much, much easier to do later on when you have some better items and a way to earn GP easily.
For now, head up some stairs to the east to reach "Dio’s Show Room", where Dio, like every rich jerk, shows off all the treasures he purchased in a vain attempt to make himself look more worldly. Investigate the Keystone display in the center of the room and Dio will show up and, after initially declining to let you use the artifact will consent… provided you entertain him by fighting in the battle arena.
At this point in time, unless you’ve prepared, you probably won’t make it very far in the Battle Arena. There are eight battles you have to win against progressively more powerful foes. After each fight a wheel will spin with random effects on it, usually detrimental. This can range from breaking your weapon (you can still attack, but with severely reduced damage), a certain type of Materia (or all of it), sealing the item command, permanently halving your HP, MP, or both, or afflicting you with a random status effect. On one hand, it might seem best to try to avoid the worst effects, but the greater the challenges you overcome, the more BP you’ll win at the end. For now, the best you can do is have Enemy Skill, HP Plus, Long Range and Mystify + Added Effect (in your armor) Materia equipped and hope for the best. If you run out of MP (shouldn’t be too easy if you went to Wutai and learned "Magic Hammer") use items like Right Arms or Dragon Scales on groups and attack singular or lesser foes in melee. If the going gets tough and you want to escape with whatever BP you have, you can use a Smoke Bomb (which can be stolen from Slaloms if you trip the alarm in Junon, along the road leading to the Underwater Reactor) to escape from battle.
The Date and the Double-Cross
For this battle, though, you need merely participate. After the battle, Dio will give you the Keystone and leave. It’s time for you to do the same. Return to the Station and you’ll find out that the lift is having some mechanical issues. Bummer. Cait Sith will show up, make a suggestion, and head off to pull some strings. Follow him to the Ghost Square and, in the hotel, the entire group will meet up and chat about the events leading up to this point. Have Cloud tell them, or decline, and either way, everybody will end up retiring for the night.
Cloud will be bothered later by whichever character; Aeris, Tifa, Barret, or Yuffie, has the highest disposition towards him, which of course depends on various dialogue options and other actions you took earlier in the game. Go on your date and afterwards you’ll return to the Station, where you’ll see a familiar face acting rather shady. After your "friend" flashes some contraband, give chase, going first into the Battle Square, then to the Speed Square, then to the Wonder Square and finally to the Chocobo Square. Head upstairs and chase the thief around the circular race registration counter, then back outside. After the package is delivered, confront the thief, who ultimately uses dirty tactics to protect the status quo.
Back in your room, search the iron maiden in the north-eastern corner of the room to score an Elixir , then exit the room and pick your party, which must include Cloud (as usual) and Aeris. Leave the Gold Saucer and hop aboard the Tiny Bronco, which you’ll need to sail east to reach the Temple of the Ancients, which is located on a small island south of Junon, and south-west of Fort Condor.
Note (Fort Condor Battle #9): Speaking of Fort Condor, pay the place a visit after you obtain the Keystone (albeit temporarily) but before entering the Temple of the Ancients to engage in another battle. After you’re victorious you’ll get another trio of Turbo Ethers .