The first battle takes place at the top of Yggdrasil, though the first two parts are scripted. The first part of the battle cannot be won, as Asmodai will use Corrupt Miasma to render himself invulnerable. He will attack the party with Blindga, Silencega and Cursed Miasma (which causes Paralysis). When he uses Upheaval, the battle ends.
The second part is also scripted. Gramps fights Asmodai on his own and the player cannot lose. Asmodai will use Corrupt Miasma and, while at first he will be invulnerable, Gramps will use Doubleshot and start doing normal damage. Asmodai will still use his status-inflicting attacks, but they will miss. Gramps will use Decisive Shot, dealing 9999 damage to Asmodai and to himself. The miasma will dissipate and the battle ends.
With his immunity gone, the party battles Asmodai for real. He may still use Blindga, Silencega and Cursed Miasma, but he will mostly use two new attacks: Forsaken, which reduces the MP of all targets and may inflict Confuse; and Caustic Spittle, which inflicts Poison, Slow and deals damage to all targets. His normal physical attack hits all targets and Upheaval does about twice as much damage.
The Warrior should be equipped with a Wind-based weapon. During the first part the player should heal as there is nothing else to do. During the second battle, the player can turn on Auto Mode and watch the battle. One can try to kill themselves, but with 0 HP, one still cannot lose.
During the real battle, a White Mage or Red Mage should cast Slow on Asmodai and the Black Mage should cast strong spells like Fira. The Summoner should call Eidolons like Sylph and Chocobo (but not Titan as Asmodai absorbs Earth attacks). The player should cast Slow again when it wears off, heal the party when necessary, and keep an eye on his strongest attack, Upheaval.
The second battle occurs below the Underground Fort. For the first few seconds Asmodai will cast Return to Darkness and make himself invisible and any attacks thrown at him will miss. Matoya will use Sense Weakness and make Asmodai reappear and the real battle begins.
Curse will inflict Curse status to a target. Earthquake and Dark will inflict moderate damage to all allies. His two strongest attacks are Return to Darkness and Upheaval, and both can hurt all party members badly. Return to Darkness will deal about the same amount of damage as Dark but it randomly inflicts a bunch of statues to all allies. Upheaval can reach as high as 1400 damage.
At the start of the battle, the player should heal and buff the party. After Asmodai re-appears for the first time, Matoya should be protected at all costs. One may need another healer besides Matoya with Curaja. It is hard to fight him with only Matoya as a healer, because Asmodai can use Return to Darkness anytime and Sense Weakness must be used to bring him back on stage. Besides Cure Waltz, one should not let her do any time-consuming dances. Asmodai can cast Curse, Earthquake and Dark after a physical attack. Curse should be cured as soon as possible. Earthquake and Dark can hurt so the party's HP must be kept high. Asmodai likes to spam Dark while he is invisible. If the party members' HP is low, especially the mages', Upheaval will be an instant-kill. The player should heal the party immediately after and never let him do it while he is invisible.
Asmodai has a wide range of attacks some of which inflict negative statuses. Forsaken reduces a small amount of MP and has a chance to inflict Confuse. Cursed Miasma may inflict Curse and Sickly Miasma may inflict various statuses. Along with his status-inflicting moves, he can use Takedown, Dark and Comet to deal damage to one target. Comet has the most damage output on a single character, exceeding 2000 damage on a level 60 party. Quake, Upheaval and Dark can damage the whole party. Upheaval can deal massive damage on all characters when combined.
The F-ability Esunaga and Ribbon are useful. IF the party members are highly leveled Asmodai's moves can't do a lot of damage. The party should include least one White Mage or Seer to cast protective spells like Shell and Esuna and Curaga.
Asmodai is an alternate spelling of Asmodeus. Asmodeus is a king of demons known from the deutero-canonical Book of Tobit, in which he is the primary antagonist. The demon is also mentioned in some Talmudic legends. He was supposed by some Renaissance Christians to be the King of the Nine Hells. Asmodeus is referred to as one of the seven princes of Hell, and in Binsfeld's classification of demons, each prince represents one of the seven deadly sins. Asmodeus is the demon of lust.