The damage is piling on the two abberations as the party continues to fight. Neither go down, but the one steadily being surrounded by the party looks very weak, at this point. Trembling all over, it still lunges to bite at Darach when he moves too close.
Spoiler: AoO on Darach
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Attack:(1d20+12)[22]
Damage: (2d6+4)[14]
Then Mercuira's arrow, bolstered by Jarome's song, digs deep into its skin, and it lets out a pained shriek. The other Destrachan, though it looks better than its companion, seems to take heed of this. Bloodthirsty as the creatures are, they're clever enough to try and get out when the odds are against them. After being hit both by Daedalus and Hastur, it lashes out with its claws - at the giant serpent, this time - before fleeing into the woods.
Spoiler: Attacks on Mallow
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Attack:(1d20+12)[17]
Damage: (1d8+4)[9]
Attack:(1d20+12)[31]
Damage: (1d8+4)[11]
Spoiler: AoO
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For Hastur and Mallow as it attempts to retreat into the woods. It acted first, so you get this AoO regardless of whether you pass the next save or not.
Completely surrounded, the remaining Destrachan opens its gaping maw and lets out an unearthly shriek.
Spoiler: Destructive Harmonics
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Everyone needs to make a Fortitude Save, DC 19. If you fail, you are stunned for 1 round and deafened for (1d6)[6] rounds.
Jarome gets the sonic resist bonus, of course.