The Ultimate Title
Written by MSG Commander
After you've obtained all the Legendary Weapons, you can face the Ultimate Boss, Apocalypse, on an island near Nolthia. To get there, go to Nolthia and fly to the southeast. Look for a small island covered with mountains. When you fly over the mountains, the game will prompt you to either attack, or leave.
Here's the strategy I used to beat Apocalypse.
Before You Start
You'll probably go through a LOT of Hi-Elixir, some Hi-Care, and a decent amount of Energi Elixir or Ether Energi. I recommend you stock up on all these potions before you take on Apocalypse. (I bought 99 of each, and I used about 35 Hi-Elixir, 15 Hi-Care, and 45 Ether Energi before the battle was over.)
I put Ash, Karim, Eclair and Enah in my party. You can use whoever you want, but train each one to Level 99, and master all Energi skills so they all have Omegadia.
Equip Ash with Fine Earring a, Eclair with Fine Earring B, Karim with a Dark Ring a, and Enah with a Light Ring a. (You can probably give Enah any old ring, though - the important thing is that they can all use Dark skills.)
Finally, when you're next to the island, but before you start the battle - Save your game. You'll most likely lose at least once, so you want to be able to reload from the point right before the battle starts.
As soon as the battle starts, have each member cast Dark Curtain on themselves. This makes all energi skills fail. (Which means you can't use Heal or Restore, but it also means Apocalypse's Alphadia, Betadia and Omegadia will miss, every time.)
Dark Curtain will remain in effect until Apocalypse uses Dark Inferno. Dark Inferno will erase Dark Curtain, cause multiple status effects such as Paralysis, Poison, Smog Eye, Sleep, etc., and occasionally lower a character's HP or EP to 1. When he uses this skill, use Hi-Care on everyone who's affected. (Try to time it so that you "cure" the next person in line, so you don't lose any turns.) If you're lucky, you'll be able to cure everyone and re-cast Dark Curtain before he uses any all out attacks. Even so, expect one person to die while you're doing all this.
Whenever a character dies, immediately use a Hi-Elixir and cast Dark Curtain. Sometimes you'll have to revive the same character two or three times in a row before you get a chance to use Dark Curtain. Don't worry about this; just keep everyone alive and capable of blocking his Omegadia and such.
He also uses skills like Big Bang, which always does 9999 damage, and occasionally uses a physical attack that could kill in one hit if your HP is low enough.
Don't worry about any of this. Just hit Apocalypse with Omegadia as often as you can, and when someone dies use a Hi-Elixir and re-cast Dark Curtain.
Don't worry about HP
The name of the game in this battle is to keep everyone alive, with Dark Curtain on, and to use Omegadia on him as often as possible. Your character's HP is irrelevant to your success in this battle. When someone dies, bring them back and use Dark Curtain. When someone's EP is too low to cast Omegadia, use an Energi Elixir or Ether Energi.
Don't bother with any attack skill other than Omegadia. Volcano, Catastrophe, Meteor Strike, etc., will all only do a few hundred points per strike. Omegadia will do around 9999 damage each time.
You'll have to use Omegadia about one hundred times in order to kill Apocalypse. (He has approximately 1,000,000 HP.) This will be a long battle, and the key to success is to be patient, to make sure everyone is protected against his Omegadia, and to hit him as often as you can. It may take multiple tries, but it can be done.
Once you defeat Apocalypse, you've completed Quest 68, The Ultimate Title. The reward for completing this quest is the Apocalypse Mark - "Proof indicating attainment of the highest title."