After Terra, Edgar, Banon, Locke, and Sabin reunite in Narshe, joined by their new companions Celes, Cyan, and Gau, they must band together to prevent the Empire from taking the Esper.
Prepare for Battle
When everyone is gathered on the mountain, you can check on each person in the line to switch places with them, allowing you to change the equipment of each person. Make sure to equip everyone with good equipment and relics. If you have the Tintinabar/Tintinnabulum, you can equip it on people before the battle to allow them to heal up without using Tonics/Potions or Potions/Hi-Potions. Don't use a Tent at the save point, because it won't heal up anyone but Terra. When you are ready to fight, save the game and talk to Banon.
The enemies in this battle can't be encountered at any other time, so if you want to learn their Rages, fight all of the listed enemies.
56. Bounty Man/BountMan/Hunting Hound
59. Rider/Hell's Rider
Organize your Parties
When you talk to Banon and say that you're ready, you will have to organize your attack parties. Here is some information to help you decide how to organize your parties. To end this battle, you will have to defeat the boss. One strategy is to can send one party directly to the boss while the other two parties block the path to the Esper in the north. The boss of this battle will often use magic attacks, so I recommend putting Celes in the party that fights him so that she can use Runic to absorb the magic. If you use that strategy, then Edgar, Celes, Sabin, and Terra make a good four-member team. Pair Locke up with Gau or Cyan, then have one party of just one member.
Another potential strategy is to have one three-member party and two two-member parties, and send the three-member party directly to the boss.
Make sure two groups are always blocking the top paths to the Esper.
Start the Battle
After forming your groups, press B to exit the Lineup screen when you are ready to start the battle. A cutscene will occur and then the enemies will start to come north. You should send your strongest party south to Kefka while the other two guard the path north to the Esper.
If you put Celes in the team that fights Kefka, she should use Runic on her first turn, then use it again after she absorbs a spell. However, if Terra is with you, and if you want Terra to use Cure, you will have to do so after Celes absorbs a spell; otherwise, Celes will just absorb Terra's Cure spell. The same is true if you want Terra to cast offensive magic; Celes's Runic will absorb the next spell whether it was cast by friend or foe. Terra could just use Potions/Hi-Potions and Tonics/Potions to get around this. Cyan should use SwdTech/Bushido 1, Sabin should use AuraBolt/Aura Cannon, Edgar should use AutoCrossbow, and Gau should use the Stray Cat Rage.
After Kefka and the soldiers leave, there is a cutscene. After this, you will have to form a party of up to four characters. You can always change which people are in your party by going back to Arvis's house in Narshe. If you want Shadow to join you later, form a party of three people, but be aware that you have to pay him to get him to join you, and he will eventually leave anyway.
If you put Locke in the party, you can see a cutscene about his past. If Celes is also with you, the cutscene changes slightly.