Achlys

Achlys /ˈæklɪs/ (Ancient Greek: Ἀχλύς "mist"), in the Hesiodic Shield of Heracles, is one of the figures depicted on Heracles' shield, perhaps representing the personification of sorrow. In Homer, achlys is the mist which fogs or blinds mortal eyes (often in death).
However in world, Achlys has been in opposition to the party seemingly from the beginning as they began to consistently face off again and again against the undead creations of Anteus, finally killing him and meeting Achlys' son for the first time Stemma. They also discover that she is the one that was lending power to Anteus for him to get his revenge and release the Grey Flood.
She would then be involved in many instances of the group being tricked with strange visions.
Eventually through the party would become more aware of the Goddess as she begins targeting Cyaro and Ghost, trying to control and manipulate them. It was at this point that they both realised that nobody could remember Achlys or much about her, except from direct interactions with the Goddess or Stemma. Later it is realised this is the result of Odysseus' actions.
Achlys uses the captured Nyx to manipulate the night around Hecate's Ravine, plunging it into darkness where the Gods could not tread, allowing Koilos to spread themselves throughout the country and starts attacking it's citizens. Eventually this leads to them setting up an attack where Typhon and Koilos would clash over Mistwater and Cyaro would be the only one capable of stopping it by bringing in the aid of the Gods. Cyaro believes that Thaem would die as he has been affected by her influence and has threatened to kill him if she does interferes with her plans. Cyaro manages to bring Thaem out of his memory and is then free to interfere.
However this turns out to be a trick and Stemma wanted them to interfere in order to bring all of a pantheon to one place and weaken them so that Achlys could abduct them and take their power. It ends up being the Cthonics who are summoned and taken.
In the final confrontation Stemma uses the powers of the Cthonics thye've captured to fight against the party, whilst Achlys tries to take full control of all of them. It is discovered here that all the children that died upon Ghost and Cyaro saying her name, had not properly passed on, but had in fact been held onto by Achlys. Upon the death of Stemma, Achlys loses her composure lost in grief, releases the souls and revealing their more basic form as a greiving child clutching her broken doll, Stemma. Cyaro sees this and decides to comfort the child and stand up for the Goddess in the face of the Cthonics judgement. During this judgement something strange happens as she is suddenly pulled into the abyss. Before disappearing she tells Cyaro "He has nothing and so will take everything!". At this point the Cthonic council seems to not remember Achlys' presence.