Silksong Theory: "Styx" is a Nosk in Disguise
1. Styx isn't "Styx"
You learn this if you jump up to the place Styx always retreats to in act 3. There, we find a great number of masks, including the one worn by "Styx." Play the Needolin and we see a memory of a headless "Styx" thinking the following: "Who To be? Who is me? The one who serves? The one who breeds? The one to fear? My strength or theirs?"
Note that this recollection doesn't use Styx's voice. Clearly the real Styx is long dead, and the thing "serving" us is something using his voice and face.
2. Skynx isn't "Skynx"
"Skynx? Who's Skynx?" You ask. Well, it's who you find if you visit Styx on Steel Soul mode. Here, Styx's nest has been destroyed, and his notably headless body lies dead. Yet destroy a hidden wall and you'll find "Skynx," a creature wearing Styx's mask upside down:
Even creepier, before we see "Skynx" we get this exchange between them and Hornet:
Hornet: "I can sense you there, hidden in the darkness. Show yourself."
???: "I can sense you. Hidden."
The creature is repeating Hornet's words back to her. Then, when it equips its mask and shows itself, it begins using Styx's voice, but with the words jumbled to create new meaning: "The morselsssss. Give them. Take." This happens every time you visit. The creature will first mimic whatever Hornet says, then appears with Styx's face and starts using Styx's words. Frighten it, and it mimics the roar of another enemy to try and scare you asay. Play music for it, and it sings using a mix of other creature's sounds. So it's a mimic with an upside-down face and two black mantis-like arms. Clearly a Nosk, right? Just one uninfected by the Radiance.
3. Skynx is Styx
Yes we see Not-Styx's headless body before meeting Skynx, but remember: Nosks don't just steal faces, they also hide in and pilot stolen bodies. Why would Team Cherry reveal Styx as a face-stealer to then replace that face-stealer with a second-face stealer that stole the first face-stealer's already-stolen face? That's just needlessly convoluted. What makes more sense is that in Steel Soul, Styx's nest was attacked and destroyed before Hornet could show up to save it. So "Styx" was forced to abandoned the body it was piloting and flee into the secret room we find.
With its nest and hoard of silk-eaters destroyed, Styx/Skynx offers to pay hornet to find fresh silk-eaters, so that it can weave a new nest from their silk.
So Who Was The Original Styx?
Probably Huntress's mate. Besides sharing the same body and mask shape, Styx's (stolen) dialogue is focused entirely around finding food for a "mistress." Presumably it was Styx's job to find food for Huntress (and the hatchlings) while she guarded the eggs, and since Styx never returned from his hunt, Huntress is forced to ask Hornet for help when they meet.
