I really know nothing of Stygian Abyss but i found this in publish 64 notes :
Encounter Improvements
* Navrey, Medusa, Stygian Dragon and the Slasher of Veils have been revamped:
o New Rewards- Night Eyes ( Glasses), Tangler (Half Apron), Venom (Bracelet), and Slither (Talisman), Lavaliere (necklace) , Mangler (Broadsword)
o Scrolls of Transcendence have been added
o Some of their stats and resists have been adjusted
o New attack added to Slasher of Veils