As far as I've seen, the 350f boss uses the moment it gets attacked and receives damage (either the immediate next action or the one after that), attacks that deal 0 damage won't trigger it. I believe he also can't use it the first 2 turns or so. I'm pretty sure he can't use it again (though the boss does Concentrate when he's really low on HP, so maybe that's what follows).
I decided to experiment a little based on this and had Aya give Tenshi first turn and immediately Direct Attack before the boss gained any ATB, then spent the rest of the turns using Concentrate. In 5 tests, 350f boss always used Scythe of Calamity and then
the next turn. With this information, I suspect that the boss has actions based on its current HP % that take priority over
, which is why I can get 3 Assassination Swords in without seeing it used, but it also uses Scythe of Calamity as a guaranteed action prior to using that attack. In retrospect, I normally see Scythe of Calamity either as an opening move or after
, likely the reason I see a delay between the two actions is because the status move is used at 75-80% of its HP or somewhere around there. There's probably one other move used based on HP between then and the
This knowledge makes it immensely easier to deal with
, because I can just bait it at the beginning with my lineup set to tank it, then switch to my damage dealing lineup. If there are no other guaranteed
uses, then I feel comfortable using Tenshi to take out the
, as it's about a 2-3HKO with World Creation Press even as a Ninja depending on her buffs, coupled with Iku's Elekiter Dragon Palace. I'll still try ***WINNER*** Satori Wand of *Destruction* DTH strats for now though.
Incidentally, the Concentrate-esque move is indeed followed up on with