After you obtain the Airship, land on Kefka's Tower to bring down the man who destroyed the world.
The lowest-level enemies that you will encounter in Kefka's Tower are level 56. It is recommended to level up until your party is near that level before you attempt Kefka's Tower.
Go to Kefka's Tower
Kefka's Tower is in the center of the southern continent. To get inside, you have to land on it with the Airship.
You will need to split up into three groups.
Group 1: Go south along the conveyor belt, then go east and follow the path until you reach a chest. Open it to get a Coronet/Hypno Crown. Then go through the door in the west wall, just south of the chest where you got the Coronet/Hypno Crown. Go west, then go south down the conveyor belt. From there, go east, then go through the door at the end.
Follow the path and open the chest to get Fixed Dice for Setzer. Go south from there to exit this area.
Go left, then south down the stairs. Continue going south, then go through the door in the east wall. You will reach a dead end.
Group 2: Go east, then south down the stairs. From there, go west and through the door in the west wall.
In the next area, go north up the stairs, then open the chest in the northwest corner to get a Minerva/Minerva Bustier. Go south from there, down the two sets of stairs, then go west. Go north through the door to reach another room, then go north in that room to find a chest. Open it to get a Tack Star/Pinwheel.
Go south from where you got the Tack Star/Pinwheel until you are in a jail cell. Go south to exit the cell. If you want to fight Atma/Ultima Buster, go into the leftmost jail cell. Atma/Ultima Buster will turn into a save point when defeated. Otherwise, go through the south door.
After you fall, go south, then west, and go up the two sets of stairs. Then go through the door on the right.
In this area, there are two tubes that you can climb into. The one on the right takes you back to the room where you got the Tack Star/Pinwheel. The tube on the left goes to a new area. In that area, go to the left and open the chest to get a Force Shld/Force Shield. Then go south down the rightmost conveyor belt. From there, go as far west as you can go, and you will find a chest that contains Force Armor. Then go east, and enter the sideways door that is just south of the conveyor belt that you came from. You will reach the room where Group 1 has been waiting. Open the chest in this room to get a Ribbon. Then step on the green switch to the left of the chest. The platform will move over, allowing Group 1 to continue. Group 2 does not need to keep standing on the green switch, so as group 2, exit this room the way that you came in, then go east and enter the door there.
Go north through the next corridor, then go north and you will find the Gold Drgn/Gold Dragon. If you protect yourselves against Lightning, you will be completely safe during the battle. Gold Drgn/Gold Dragon is weak to Water.
After fighting (or ignoring) the Gold Drgn/Gold Dragon, go through the door to the left. Follow the straightforward path through the next room. Then go up the stairs and continue going north until you find a green switch. Step on it, then switch to Group 1.
Group 1: Go south along the path appeared when Group 2 stepped on the switch. In the next room, equip your people with Safety Bits and Memento Rings/Safety Rings, and equip Relm with a FakeMustache/Fake Moustache if she is with you, and go east. Against Sky Base/Death Machine, try using Relm's Control, and use Doom on it to get rid of it quickly.
Keep going east through the capsule room, then go through the east door.
Go north, then east, then south through the door. From there, go east, and walk north onto the broken conveyor belt.
Group 3: Go south then go west and open the chest to get a Red Cap. Then go north through the door. Continue going north, then open the chest to get a Nutkin Suit. Go east from that chest to find another chest. This one contains a Gauntlet.
Go back the way you came until you are in the first room of Kefka's Tower, and go southeast, then go south, and go through the door at the end. In the next room, go west through the door.
Open the nearby chest to get a Hero Ring/Hero's Ring. Then go north and walk onto the conveyor belt. In the next room, go west, under the bridge, and use the save point if you wish. Then continue going west and you will have to fight Inferno.
I recommend focusing all attacks on Inferno, and not on the arms. This is because there is a risk that if you kill one of the arms, Inferno will use Meteor, which will kill everybody unless you're lucky.
An alternate strategy is to use Wall Rings/Reflect Rings to bounce Inferno's Lightning-elemental spells back at it, but only if Mog or Strago (if he knows Pearl Wind/White Wind) is with you. That way, you can still be healed even though magic cannot be used on you. If you use this strategy and Mog is with you, have him use Wind Song/Wind Rhapsody. However, as mentioned in the previous paragraph, this could result in Inferno using Meteor and killing everybody.
After Inferno is gone, go south through the door, and continue going south until you are back in the first room of Kefka's Tower. Go southeast and open the chest to get a Megalixir. Then go southwest. Check on the sparkle to fix the walkway that Group 1 is waiting on. Then go up the conveyor belt and open the chest to get the Rainbow Brsh/Rainbow Brush. Go north up the next conveyor belt, then go back the way you came. Go through the door to the right of the sparkle that you checked on earlier.
Keep going north and you will find the Skull Drgn/SkulDrgn/Skull Dragon. After fighting or ignoring it, go through the door in the north wall. Follow the path around, and you will be outside in the area where Group 2 has been standing on a switch. Go north and stand on the green switch on your side. The center door will open.
Group 1: Go north on the walkway that was fixed earlier when the other group checked on the sparkle. Afterward, go northwest and open the chest to get a Tack Star/Pinwheel. Then go east, then north and through the door. Continue going north, through the door that the others opened by stepping on the two green switches. In the next room, you will have no choice but to step on the center green switch. After that, go to the left, then go south through the door. Make the other group get off of the switch down below, then switch back and check on the 4T weight. You will push it onto the switch, and the stairs on the left will become accessible. After this, walk north and then step on the green switch at the top.
Group 2: Make sure that everyone is equipped, then go up the stairs that just became accessible, and go north through the door. Go to the right, then go south. While outside, make the other group get off of the switch, then switch back and check on the 4T weight. You will push it onto the switch, and the stairs on the right will become accessible. After this, walk north and then step on the green switch at the top.
Group 3: Go up the stairs that just became accessible, then go north through the middle door. Step on the middle switch. Stairs will appear, leading to a door in the middle of the north wall. Before going through that door, go south through the door, and you will be on the upper ledge. Step on the switch here to make new doors appear on the sides. Groups 1 and 2 can use those later, but for now, go north after making those doors appear, and keep going north. You will have to face Guardian, which imitates several bosses, including Ultros. Put everyone in the back row to prevent getting killed by Ultros's Tentacle. I also recommend equipping the RunningShoes/Hermes Sandals on everybody to prevent Entwine from causing Slow.
Guardian is weak to Lightning-elemental attacks. Throughout the battle, Guardian will imitate bosses that you have faced before: Ultros, Dadaluma, Air Force, and AtmaWeapon/AtmaWepn/Ultima Weapon.
After this, use the save point if you wish, then go north through the door. From there, go to the left, and then south through the door. From there, go east, then north. Above you is one of the Warring Triad statues. Check on it and you will have to fight Poltrgeist/Poltrgst/Demon.
Poltrgeist/Poltrgst/Demon is weak to Poison-elemental attacks. It is vulnerable to Stop. Once its HP is 32640 or lower, it will start using attacks like Meteo/Meteor and S. Cross/Southern Cross.
After the battle, the statue disappears, and you are knocked back. Go north through the door. There is a save point, and then a hole in the floor. Fall through the hole, then go north and step on the green switch.
Group 1: Go south until you are outside, then go to the left, and then go through the leftmost door. Continue going north and you will encounter the next Warring Triad statue, Doom/Fiend.
Doom/Fiend is only weak to Pearl/Holy, and it absorbs Ice and Poison. Doom/Fiend is the only enemy in the game to use Force Field, a Lore that Strago can learn.
Doom/Fiend uses Ice attacks, so you might want to equip protection against Ice.
After Doom/Fiend's HP is 32640 or lower, it will get the statuses Image, Haste, and Reflect. It will also start using the move Targeting, which targets a character in your lineup. Then Doom/Fiend will use Demon Rage/Fiendish Rage on the targeted character.
Afterward, the statue disappears and is replaced with a save point. When you are ready, go north through the tube, then go north and step on the green switch.
Group 3: Go south until you are outside, then go east and then through the rightmost door. Go north and you will reach the final statue, Goddess. Equip Safety Bits and the Memento Ring on as many of your characters as you can. Also equip protection from Lightning. Equip the Offering/Master's Scroll on someone if you have it.
Goddess has no elemental weaknesses and absorbs Lightning and Pearl/Holy. Goddess can use Love Token/Overture, which causes a member of your party to be damaged instead of Goddess if you try to hit her.
Goddess can cause Entice on your party. Entice is similar to Muddle/Confuse, but it can't be prevented with a Ribbon or any other equipment, and can't be healed. If possible, use spells like Flare and Ultimathat ignore defense.
After you hit Goddess eight times, she uses Overcast/Cloudy Heaven. This inflicts Doom on everybody, and from that point on, anyone who dies becomes a zombie instead of being KOed.
Try to defeat Goddess as quickly as possible.
After the battle, a save point appears, and you can access the doors behind the statue. Save and go through the doors. If you step on the third green switch in the next room, you will begin the Final Battle.