The cavern has been flooding and drowning things for longer than Sylvaine has been down here, and she stopped fighting the process a long time ago. What she raises out of the silt does the fighting for her, and dying near you is the whole point.
A weak disposable minion rises near a random enemy - real Blighter Animate Dead, scripted directly rather than left to AI, since the payoff depends on exactly where and when it dies.
That PC banks a stacking spore (a minor Strength drain). No other boss in this bestiary spreads a status off something ELSE dying - every prior mark or curse here is applied directly by the boss to a target it chose.
Everyone else within 3m of that PC also takes a spore, and the bloomed PC's own count clears. Clustering near a dying husk is the actual danger, not the husk itself.
Two Bloom Husks rise at once instead of one - the same verb as her ordinary spell, doubled, at a real capstone moment rather than a generic autocast.
Flooded Cavern's real ceiling was Kessa Wavemother at CR15 (round 6, singular area - distinct from the plural Flooded Caverns which hosts Xanthir Mor); Sylvaine is pitched one notch above at CR16, into 3 of the area's free Sparky slots.
She is the bestiary's first Blighter - and the first boss this round drawing from a REAL dedicated spells.2da column rather than a Wiz_Sorc-filtered fallback: Cultist/Nentyar/Telflammar/Domiel/Sohei/Bahamut/Blackguard/Chalice/MiddleCircle/SoLight/Blighter/Healer/Shaman are the only PRC-added columns confirmed to exist in this hak's own table, checked by reading the header row directly rather than assumed. Its own list already runs Animate Dead / Create Undead / Vampiric Touch / Finger of Death without any filtering needed - genuinely, natively necromantic nature magic.
Real Epic Spell: Mummy Dust (id 637/874) - the only one of the five that pairs perfectly with its host's ordinary class spells (Animate Dead, Create Undead) rather than sitting apart from them; the capstone is the exact same verb as her round-to-round mechanic, just doubled.