so Neph literally gets stronger as people simp for her? Amazing, Sunny bout to make her divine all on his own.

Do you remember Ananke's story? While she was a child, she told Sunny about outsiders who gave birth to a child, but couldn't leave her to her fate as a riverborn. So they used their flying magic ship, which somehow allowed them to ignore the rivers normal effect on the riverborn. Since we know time is looping to some degree (hence the mad prince and friends existing), it's not unlikely that child is Effies and the ship the Chainbreaker. Honestly considering time loops in a whirlpool, there's a good chance the end of the river(past) loops to the beginning (future) and that everything we're seeing has happened before

I'm guessing it's a Lord of the Mysteries type deal - the components necessary to reach the next level involve consuming those at the same level (would explain them betraying Nephs dad too). Something like "to enter the 4th/5th nightmare, you must take the essence of a Saint/Sovereign"

I'd imagine it's more an arrow for Saint to fire with Morgans warbow after she's become a Saint.

I thought all echos of Sunnys could become shadows? Like even the Carapace monster from the start could have been converted