Any tank without magic defense gear will almost instantly die. Do not rely on stuns or staggers. Aegis PLD is ultra highly recommended. Erratic Flutter must be dispeled. Buff everyone with fire carol and bar fire.
Appears to have a Dia aura. Don't waste mp dispelling dia, just keep regens up and cures.
WHM99/BLM49 with trusts
Insanely difficult and virtually impossible under normal circumstances, but fairly easy with a party of PCs or the correct party of trusts. Mob takes ANY DoT or debuff effect and uses Exuviation to convert them into massive HP for itself. A single DoT/debuff will give it 6k HP and stack for each DoT/debuff, even if the debuff is resisted or wears off. So it is critical that the party uses absolutely nothing that will DoT/debuff the mob. In my case, I went through a ton of trust combinations until I found the correct ones that worked...basically the most boring trusts that do the fewest and least impactful abilities but still hit hard.
Valaineral (tank, do NOT use Gessho, he uses a debuff ability), Naji, Abquhbah, Prishe II, Klara, myself for WHM. I healed Valaineral so he could keep his MP, and used Spirit Taker to refill my MP. Most WHM trusts use paralyze and slow, so be sure your trust will not use any debuff/DoT spells.
Barfira is also critical as mob uses Firaja multiple times (which stacks), other Fire spells, Fire Break, and Erratic Flutter (fire based). Also be sure to cast your trusts with the best gear on so their stats mimic your own. This will help their resistance to Fire. Erratic flutter and Erosion Dust does NOT need to be erased as there is nothing to erase.
If you avoid debuffs/DoT correctly, Exuviation will heal the mob for 0 HP. One debuff/DoT is manageable as 6k won't heal it for too much to set you back too far. Anything more will seriously hurt your progress which is bad because you have 30 minutes to kill both mobs.