I see it has not been posted once so far so here I go.
The Boss Blitz Boss Songakshi is currently bugged, effecting mostly Calamity level 7 and 6. With the attempt at a bug fix this last September, a new attack pattern was created, one shotting players with no warnings.
1) Have Songakshi in her regular attacks (knife strikes, melee etc)
2) Suddenly, no prior warning, she will do a sort of square / box AoE in front of her, looking like a rectangular Black Wave.
3) After less than 0.3 seconds delay if you remain in the AoE, you take MASSIVE damage, immediately 1 shotting you.
4) No red box warning, in-between her auto-attack and done extremely quickly with little tells.
5) It happens at any phase of the boss. From the start to the end
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Do note that she is also still desyncing and lying on her face direction after ghosting out.