BOSS ANALYSIS : Again, nothing new comin’ from Dark Bahamut, other than attachments to his attacks. There is the usual basic physical, which will be his main attack. After every five attacks that hits Dark Bahamut (excluding counters, to be noted more momentarily), he’ll use Impulse - this is unblockable damage to everyone, and it will also dole out Slow, Petrification, and the Power, Armor, Mental, and Magic Breaks to halve your stats. As predictable as ever, Dark Bahamut will use Mega Flare when his Overdrive gauge is full, hitting everyone very heavily with a basic Dispel effect.
MAIN STRATEGY : Either you have Ribbon, abuse counterattacks (to be mentioned), or die. That’s it. You can’t win in five Attacks unless you somehow manage to hit for 800,000 HP each time. And while that’s readily possible through Wakka’s 2x-2x-2x Attack Reels (12 hits), you’ll need to exceed 66,667 damage on EACH of those hits, all against an enemy with 234 Defense. Any less than that twelve from Wakka equals a failure there. So, yeah, multi-Overdrive works, but that’s not very reliable, especially against a 255-Agility enemy.
So, you don’t wanna super-duper-mega-Overdrive this guy, and you don’t want to go for counterattack abuse. Fine then. Be my guest. Auto-Protect will be great for this battle, or at least a regular Protect - the only thing that’ll get rid of it is Mega Flare, and you can predict that; Impulse nullifies it, but you can Dispel it (and reinstill Protect if it’s not Auto’d). Hyper Mighty G is sa nice way to open for quick Protect, Haste, Regen, and Auto-Life to all; if you would prefer to instill those manually or already have them Auto’d, then you need to go for Ultra NulAll, as those five Cheers will be hugely helpful in lessening the damage from the Attacks you’ll be pummeled with. It makes Attack survivable, and Impulse already is, so there’s Auto-X-Potion doing its work for you.
So, basically, all you have to do after that buffing is to use lots and lots of Quick Hit, and Dispel any Breaks you get hit with, and send in Aeon fodder when Mega Flare’s comin’.
ALTERNATE METHOD - COUNTERATTACK ABUSE : Simple enough, since you’ve probably used this strategy once before if you’ve used this FAQ. As you know, Impulse is triggered whenever five attacks are sent Dark Bahamut’s way, right? With Ribbon and Auto-Haste, it’s a bit of an inconvenience since you have to deal with the Full Break, although it’s a LOT worse without Ribbon (instant Game Over). If you’re unwilling to bother with 297 of Dark Matters for Ribbon on the party, or don’t have the Defense/HP necessary to stand up to Attack, or the Agility to get in the buffs needed to stand up to Attack first, then this is for you!
Evade & Counter. Yup. That’s it. That really ought to work. You can also try working Sentinel Specials with a Counterattack character that has Auto-Potion (with X-Potions), Auto-Protect, and a nice bit of Defense to see how that works; it basically quarters the damage, which is better for those of you with lower HP/Defense. Either way, the counterattacks won’t trigger Impulse, meaning Dark Bahamut is essentially killing himself. Just keep Yuna out of the main party so you can switch to her when Dark Bahamut’s Overdrive is full to provide some cannon fodder for Mega Flare.
As usual, Overdrive Abuse works very well.