First, you get all of your characters around level 60-65. You must have a Devout, a Summoner, a Black Belt, and a Ninja in your party. Put your mages in the back row, and make sure that the devout has every white Magic spell in his/her spell book. Then make sure that your summoner has every summon magic available for use.
The Cloud of Darkness attacks four times each round. It swipes its hand at your, uses bad breath, casts the spells haste and protect on itself, and uses lightning. After you deplete a portion of it's health, it starts using Particle Beam a lot.
The party should have the best armor and weapons equipped, and you want good defense and magical defense. Everyone should have their share of either ribbons, aegis shields, or onion armor so the bad breath attack won't affect them.
Use Arise when ever needed, and when not needed, use Curaja and Curaga every turn. When you use Arise, have everyone else that is standing use an elixir so they won't die. Intend to use up all of your shuriken and elixirs. I killed The Cloud of darkness in about 8 rounds using this technique, and this party at Level 66:
Arc: Summoner
Luneth: Black Belt
Refia: Devout
Ingus: Ninja
