What to do at the end of the true pandemonium Istaroth fight (the version unlocked after defeating Satan)?.
I don't see the mass hypnosis move in the SHIFT menu (only 2 adjust formations, guess either the game is bugged or I need to do something else to let the move show up), and Istaroth just regens back when I wipe out his health. Have no clue what should I do.
Update: After hours of pain, I finally did it!!!!! This fight is exponentially harder than the Satan fight. Just in case if someone else has the same issue, the whole fight essentially has two phases.
For phases 1, essentially level up every member to be as high as possible (preferable max level 55, does not take long with a tome of discipline equipped and elixir uses), and get max dark defence (armour + amulet + tome with dark resistance, at least 2 out of 3), then try to fix field attribute to Dark throughout the fight (turmoil & protagonist special skill), to manipulate Istaroth's AI (he tends to only use Dark attack when field attribute is Dark). The first 3 turns are the hardest. The general gist is Awaken Irito in turn 1, stance and super-strength (from Jueli or Protagonist) in turn 2 and then uses exorcist's slash in turn 3 to wipe out the 4 orbs and 2 Zenan brothers (should do 3000+ damage to each). If the first 3 turns go right (at least 3 characters are alive, including Irito and one who can resurrect others), the rest is a straightforward loop of super-strength, stance, exorcist's slash/golden slash (after awakening effect expires). The points of the other 4 characters are either heal or buff, instead of doing offence. With some optimization of character skills & equipment, I am able to pass this phase for~50% of the time.
Also, the boss does not seem to inflict pronant anymore, which means no need for pronant resistant gear. In general phase 1 is around subverting player expectation. The same strategies that worked for previous bosses (fixing field attribute to be light/fire) no longer works, with fire especially being a trap that seems to work at first few tries despite being a suboptimal strategy (same offence compared to golden slash, yet more defence is required).
For phase 2, if the characters' dark defence is high enough, enemy dark miasma does 0/1 damage only. The prompt of "Mass Hypnosis" is weird, probably a mistranslation. But essentially you need to get rid of the 20 breaks (equip area attack spell for each character beforehand, Dogo special is especially useful as it attacks all enemies twice, can knock out 10 break points with single skill), then awaken choice will come back in the SHIFT menu, then you want to awaken protagonist 4 turns in a row, then wait for one extra turn (at least for me, maybe it is a bug). The attack crystal burst will then show up, and this attack kills Istaroth in one hit, ending the fight. The difficult part in this phase is the Israroth pillar attack that does increasing damage and number of hits as the turns pass (1 hit 150 damage at start, 4 hits at ~350 damage 4 turns later...). The only counterplay is to pray to RNG god that Istaroth does not target the Protagonist multiple times in a row, and try to have Serafina special ready (might not need it, but good insurance if used right). For other characters, defend & heal/resurrect only (though I failed to notice significant damage drop after using defend option, defend might not reduce damage for the pillar attack, need confirmation).
I think that it might be possible to do the fight at a much lower level (~40 for each member) through different field attribute choices (when there's no field attribute & Earth, Istaroth also seems to mostly use Dark attack.). I haven't tested the wind field attribute yet, but if Istaroth does not use any wind attack, then Jueil + Turmoil based wind strategy can probably be employed to reduce defence stat & equipment requirements. It might also be possible to inflict debuffs on Istaroth, It is probably unlikely, but it would be pretty funny & rewarding if he can be poisoned & sealed... I also never used Auto heal, therefore there's another piece of potential optimization. Considering I wrote a whole essay describing fighting him at max level, I will probably not bother doing the same fight at level ~40... Perhaps no one will...
Update 2: Apparently this version of Istaroth is different from regular phase 3 Istaroth. Regular phase 3 Istaroth is a glass cannon that can be killed easily in 2 hits (the key being land 1st Exorcist slash ASAP by getting Irito buffs ready right before entering phase 3). This version, however, has more defence & health pool...