BD challenge playthrough: Finished!
So I did the Dimension's Hasp, which I made harder on myself than necessary because I forgot to stock up on items. Generally it was pretty easy, Dark Nebula kablooie takes out all but high-defence enemies and Pressure Point can deal with those, although Guzzlers near the bottom (great durability, nasty ST physicals which status, but often run away) were a problem certainly. Walking out isn't terribly exciting either. Oh well, I got all the ultimate weapons etc.
Final dungeon is easier, largely gets curbstomped, same strategy applies, yay a Ribbon. Let's talk about bosses.
Flying Fairy (9+2 resets)
First of all, the "+2" is because the game froze during this fight, twice. Apparently it's a known issue and can happen during long fights for some reason, and turning off the power between attempts can help, or something. So says the internet anyway. Oh well. I will note that one time it froze, it did during the animation of Slaughter with a 9999 clearly visible on the screen. I'm pretty doubtful I would have won that attempt anyway. (The other... maybe? It was one of my later attempts.)
This fight is extremely difficult because our dear fairy can pull out huge damage to either defence without too much warning. Skillset specifics:
-Acedia: As before. Removes Spellblade and all other buffs. It does NOT remove Absorb Magic, which is good because otherwise I dunno if I could win this at my level.
-Slaughter: Again, huge 10-hit physical to random targets, poisons, can kill three non-defaulting PCs from full HP in one go, can certainly wreck defaulting PCs too though not a party of them. 1 BP cost. If my party's in bad shape and this gets used it's GG, so keeping the party in good shape is important / if I'm not in good shape I just have to pray she doesn't use it while I patch things up.
-Zeta-Flare: Fire damage to everyone, blah blah blah see Flare from the previous fight. It's the only element she uses this time, so Iceflame Shields null it when Acedia isn't in effect.
-Dark Abyss: Dread to everyone. She doesn't use this often, but it's bad enough to justify fear blocking on most people, partially because of...
-Plague: Kills anyone with a negative status, MT, doesn't care about status immunity or Absorb Magic. Only used if someone is statused, and then not always by any means, so there's no real way to abuse this unlike Poison Punisher, at least that I could figure out.
-Default: Next turn is Acedia + Zeta-Flare, which does high 2HKO damage to anyone Defaulting and dispels/makes weak to any future Zeta-Flares. The good news is that Default is ALWAYS followed by this, so there's some predictability which can be abused.
So here, in principle, is what I try to do. First of all, healing is important. Drain + Minus Strike is the best way to do it, and as soon as I have at least 1 BP and I'm injured, that's the plan. Drain being frequently removed by Acedia is bad, but there's not too much I can do about it. I have Slow & Steady (Spd+50% for the turn after using Default) on three people so after defaulting I'm ensured to go first, and this helps with surviving attacks some... although it's not perfect. On a turn I can heal, Slaughter can be used, which does huge damage. Same with Zeta-Flare if I'm currently under Acedia. If I have spare BP I can use Absorb Magic to hopefully protect myself from that.
Secondly, keeping her attack as low as posisble is a big deal. I try very hard to use Defang at least every three turns. What Slaughter does is random and unpredictable, but it's less bad the lower her attack is, of course. (It's always bad.) Of course, a turn using Defang is a turn not Defaulting, so I try to do Defang on "safe" turns, that is, either when her BP is at 1 (so she's about to use Zeta-Flare for sure) or -1 (she just used Slaughter). But if the status is about to expire I'll do it again, more dangerously, if necessary. Unless I don't have the turns to do so and every turn is going to surviving (healing, reviving, removing statuses, using Absorb Magic, etc.)
Finally, when she Defaults, the three PCs who have it use Absorb Magic, since that will null Zeta-Flare. Since they're totally safe that turn (aside from Acedia's effects), then can also safely use those turns to heal, heal status, or use Defang as necessary.
After a bunch of my resets I grind for three extra fights to get Minus Strike on all four of my PCs, since trying to heal with other things just isn't good enough here. Also, the last PC to get Minus Strike is my Monk, who can then adopt a setup of HP+50%, Minus Strike and Phoenix Flight (deal damage equal to current HP, lose that HP... but drain spellblade restores it) to do pretty big damage, which is nice. This is my one PC without Absorb Magic still, so he has to Default when she has BP, and try to recover next turn.
Lastly, there's the issue of MT Dread. I have two PCs with Courage Rings blocking it, and one with a Ribbon. The last PC I have switch between an Aegis Shield to block it, and an Iceflame Shield to block Zeta-Flare. My strategy is generally to only use the Iceflame Shield both when I'm not suffering from Acedia (so that it actually does something) and the Aegis Shield otherwise, or when my BP is 2 or higher (and thus losing that BP would suck). I remove shields for some Rage attacks with the two PCs who have that, which is always a bit dicy but the damage is hard to argue with.
Healing poison/dread with a PC who defaulted the previous turn is also kinda handy, since it can cause her to use Plague and have it miss. Best not to count on her doing that, though.
That's about it! Very tough fight but ultimately manageable.
Ouroburos
No resets here. While I wouldn't call this a trivial fight, it's much easier than the previous ones.
Main setup difference is ID immunity on everyone. (Ribbon user has Hermes Shoes.) I had more changes planned had I lost my first attempt, but this never became necessary.
The first form, with my jobs at least, can Minus Strike for a OHKO, or Quigong Wave for heavy default-piercing damage (borderline OHKO at first, until I start using Defang), or use Nothing Ventured and kill multiple people on counters. I learn never to attack with more than one. He also uses Death Spellblade but lol. Anyway once I learn about the counterstance I'm in no danger of dying thereafter since the worst he can do is kill one PC a turn, that never works for a solo BD boss.
Second form is a complete joke, ID and nothing else. Oh no some weakass physicals.
Third form is also a joke. It has an attack called Demonic Touch which lowers all BP by 1, MT. Basically, this trades one of his turns for one of all my PCs', which is largely neutral. The main thing is that if I just acted down to -1, this will make it -2 and I won't be able to Default or otherwise act next turn, which is potentially bad, so I start trying to go down no lower than 0. If I'd had to learn this during form 5, it could have been a problem.
Fourth form is now only mostly a joke; but he'll use Armageddon, a powerful (potentially OHKO) MT magic attack when his HP is lowered enough. It also fully heals him but the battle ends after he uses it a third time. Since he can only use it after he's beaten up a lot, I can anticipate it, and learn that yes, Absorb Magic nulls it, so there's that. There's also Celestial Touch which boosts his damage, so I can Defang a bunch to weaken his physical back down. Not much I can do about its effect on the magic, but it still doesn't OHKO through Default or anything (though it's a bit dangerously close to my lower-HP PCs).
The instant death continues throughout all the forms and is a wasted turn forever.
Okay let's talk about form 5 since it can actually win without relying on me being incompetent.
Form 5's big new trick is Disaster, which is pretty much a clone of Armageddon. That's bad.
But it no longer heals him at least! That's good.
But it's still a MT OHKO attack, and is now used without warning. That's bad.
But I can stop it with Absorb Magic. That's good!
But I can't spam Absorb Magic all day; I need to attack periodically and besides Demonic Touch would wreck me then. That's bad.
But I don't need to, because I can survive it under Default. That's good!
And if I'm injured, I can safely heal with Drain/Minus Strike, used with Absorb Magic on the same turn, so I won't die due to not defaulting. That's also good!
And he never dispels, so I don't even have to recast Drain often. Even better!
His other trick is Divergence, which basically forces me to Default for the next two turns (or summon friend, not that I do that. Challenges don't need friends!). That's really not too bad, if he uses Disaster on both those turns I can die but whatever, Absorb Magic Phoenix Down strats exist. In general I use Absorb Magic on most turns I'm not defaulting, at least with the three PCs who have it. The monk just accepts being beaten up and Minus Striking really hard to get it back.
And that's really about it! The rest of his skillset is pretty junky outside of explots I've already mentioned. Minus Strike/Phoenix Flight combos, and Dark Nebula using the dragon-slaying ultimate katana, Murakumo (either does 6-7k or criticals for 9999) provide my damage workhorse that isn't healing. I just keep Dark Shields on everyone because elements and status no longer matter. I do Defang him occasionally but it's not really a high priority, the physical isn't that bad anyway. He has notably less HP than the previous boss (a third less, to be precise) and in fact not all that much more than Gigas Lich 5, so that helps.
So many worthless scenes to skip in this fight.
So yeah, challenge complete. I was Level 75, roughly.
I may post some stuff about the five jobs I played with, but later. It was a lot of fun! Definitely recomend this challenge to others, for all that you shouldn't play on Hard Mode unless you are crazy.