One of the largest and most powerful drake species, ether drakes made their way from the Ethereal Plane to the Material generations and generations ago. But they still retain psychic powers from their time on the esoteric plane. They may not be as malevolent as many other drakes…but at CR 10, with the usual drake speed and the added ability to condense ether around their victims, they don’t have to be.
Haunted by mistakes from his mortal life, a spiritualist’s phantom urges his mortal companion to challenge beasts that toe the line between the Material and Ethereal Planes. The spiritualist recruits a party of adventurers to head into the Barrowlands, so that he may test himself against the ether drakes that have a nesting ground there.
On the world of Overhaze, the Ethereal and Material planes aren't separate. Rather, the Material Plane juts out of the Ethereal in the form of mountain ranges of reality poking above the cloud-covered spirit world. Adventurers who descend into the Haze face enough number of threats, from roving spectres to mindlinked rampages of ether drakes that coordinate in silent and stunningly effective strikes.
Save a saint? That’s no small order. But when the request comes from the lips of a reincarnated St. Brendan the Navigator, who has left the afterlife in order to see this mission fulfilled, what else can a group of Catholic clerics do? Saint Columba’s soul has been stolen from Heaven, and divination reveals it has been spirited to an island in the North Atlantic. St. Brendan believes he knows which one—a mist-shrouded isle from his travels that he never told any chronicler about, for fear that others might mimic his journey. The beach is indifferently guarded by ether drakes; more dangerous creatures—and otherworldly temptations—lie further inland.
—Pathfinder Bestiary 5 99
Yes, I just listened to the audiobook of Jim Butcher’s The Aeronaut's Windlass. That second seed owes a little to the mysterious setting of that book.