Gimme them hot Murakumo 3 tips. After months of on/off grind I'm just about ready to start working toward beating it. I already know its arms respawn on turn intervals of +1 each death but there's obviously a lot more than just that happening here.
This is what I ended up with after observing its AI for a few fights.
Did some more runs on 30f to study its AI. This is what I've determined.
Spoiler:
Living God: Ama no Murakumo no Tsurugi
Random Actions: Magic Drain, Destroy Magic, Spirit Drain (halve TP), Destroy Spirit (TP to 0), Black Universe, Time-Space Warp, Golden Protection, World-Shaking Military Rule, Oracle of Sacred Mirror Dedication, Oracle of Eternal Heaven and Earth
Oracle of Eternal Heaven and Earth appears to be used more frequently when there are more debuffs present, which is how it worked in the 20 enhanced Murakumo fight, but it can be used when there are no debuffs present. Similarly, Oracle of Sacred Mirror Dedication can be used when Murakumo is at full health.
Turn 1: Random
Turn 2: Random
Turn 3: Godly Scarlet Gold Slash
Turn 4: Random
Turn 5: Random
Turn 6: Yakumo's Futsu no Mitami no Tsurugi
Turn 7: Random
Turn 8: Random
Turn 9: Great Destruction
Repeat Turn 1-8
Turn 9: Great Catastrophe
Repeat Turn 1-8
Turn 9: Great Despair (Frontline TP to 0)
Repeat (I haven't gone any further so I can't confirm if it does repeat or not)
Reviving Arms does not advance this pattern.
Living God's Right Arm:
Random Actions: Dividing Slash, Instant Death Attack
Turn 1: Random
Turn 2: Greatsword of Calamity
Turn 3: Random
Turn 4: Greatsword of Calamity
Turn 5: Random
Turn 6: Scythe of Calamity
Turn 7: Random
Turn 8: True Greatsword of Calamity
Turn 9: Random
Turn 10: World-Shaking Military Rule
Turn 11: Ama no Murakumo no Tsurugi's Wild Dance
Repeat
Living God's Left Arm
Random Actions: Red Curse, Blue Curse, Purple Curse, Green Curse, Yellow Curse
Turn 1: Random
Turn 2: Storm of Light Particles
Turn 3: Random
Turn 4: Storm of Light Particles
Turn 5: Random
Turn 6: Great Tree that Descended from the Sky
Turn 7: Random
Turn 8: Shining Arrows from the Sky
Turn 9: Random
Turn 10: Magical Blast
Turn 11: MAG Up
Turn 12: Random
Repeat
When the Arms are defeated and revived, their AI pattern resets to the beginning.
I incorrectly observed the revival pattern, so I cut that out from the quote.
Probably the biggest issue, besides balancing attacking the Arms and Murakumo, is that guaranteed use of Yakumo's Futsu no Mitami no Tsurugi, which heals 1% of Murakumo's HP for every 1 MP it drains (drains half the target's MP). The first use isn't too bad since you're probably still working on racking up Arm kills, but uses after that have the potential to heal a huge amount of HP if you don't put a low MP character on the leftmost slot. Also, if you have difficulty defeating the Right Arm, then facing repeated Greatsword of Calamity uses can be very dangerous for such a long-term fight. Don't let it survive long enough to use True Greatsword of Calamity, that's basically an instant death attack. The Left Arm isn't very dangerous, and is also susceptible to PAR. PAR can help prevent Left Arm from acting right after Murakumo uses Great Destruction, which has the potential to be very dangerous with all of its MT attacks. Otherwise, its only notable attack is Shining Arrows from the Sky, which is just a decently strong MT attack. Right Arm has high DEF and average MND, vice versa for Left Arm. Right Arm is weak to NTR and SPI, Left Arm FIR and DRK. Murakumo has no weakness and resists SPI and DRK.
I neglected to mention it in the post I quoted, but Murakumo's Godly Scarlet Gold Slash and Yakumo's Tsurugi always target the leftmost slot, and so does Right Arm's (True) Greatsword of Calamity.
Ah yeah, also, defeating either Arm weakens Murakumo's counter, defeating Right Arm removes the DRK component, Left Arm the SPI component. Defeating both Arms turns Murakumo's Counter into a basic Direct Counter.