There is a theory going around that the Red King and Pa Wraith are also starborn.
"Going around..."
where?
Haven't seen it here.
... Evidence for this is a) for Pa Wraith the outsider protection thing he has. According to the theory he was a starborn of a previous cycle. Hence his expertise on starborn. He was sacrificed and came back with something extra. The defense thing he has.
Pretty sure it's wrong for Raith Père -- think I read WoJ stating that he just
this cycle became aware of the whole "Starborn cycle" / Outsider thing, & decided he wanted to become a power-player, acting-upon instead of acted-upon... that's why he has such a substantive library: he was educating himself.
... As for the Red King his entire motif just gives outsider vibes. Lord of the outer night. Anyone? ...
But it's not just the RK -- his inner circle was the "Lords of the Outer Night" (I call them LOONs)
That said, "Outsiders" and "Outer Night"
may just be coincidental, or may
not be -- I'm very suspicious of this, myself! I
do tend to think there's a connection, though I'm not absolutely convinced of one.
We also have the WoJ that the LOONs got so powerful because they actually were able to capture (and addict to their venom) the beings that the Mayans
had been worshiping as gods.
I think the Ramp's are creatures of the Nevernever, natively; I note several similarities in the descriptions of the native-form (without fleshmask) Ramps, and the Ick... and suspect them of being related entities.
I think some long-ago Maya (or maybe Olmec... or even older) sorceror was exploring the deep Nevernever and got possessed -- or maybe summoned one, and got attacked/infected; thus becoming the Red King. IIRC WoJ says the Red King was about 6K years old...?
How all of that might play into an Outsider connection escapes me; maybe one (or both) of my theories is wrong, or maybe it's as simple as Ramp entities being every bit as susceptible to Outsider influence/possession as humans are...
... It also explains a lot of things such as why Harry keeps getting things that whisper in his head. First Lash and now the mantle. Its Uriel helping to prepare Harry for whats to come.
I think Lash & the mantle
are both training-up Harry's willpower, yes!
But we've already seen that many Outsiders use psychic attacks, I don't think we need to look for another "possession" in the BAT: I bet Harry has to face off against multiple psychic Outsider attacks at one time.