Cor destroys.
But he has a really good reason.
He destroys, and he moves.
"Uh... a ways. You probably don't wanna walk it. I'm not even sure I wanna fly there."
He contemplates this state of affairs for a moment, and then the whole hill shudders delicately and starts sliding across the ground. (Tias grins the grin of somebody who is really enjoying his newfound capacity to scoot hills.)
They zoom across the wasteland, leaving the dissipating clouds behind. Tias giggles and lets the wind of their passage ruffle his feathers.
The mountain is indeed pretty small, more of an unusually large rocky hill than anything. When they arrive, Tias steers the hill partway around it, and points at an arched gap in the rocks near ground level. "There's like a... almost a house in there," he says. "With mystery stuff in it. I'm gonna go check it out."
He takes off and glides down to the opening, then walks in. It's tall enough to admit him, even though he is himself pretty tall.
The archway leads to a tunnel which leads, eventually, to a room. It's kind of dim in there, at least until Tias starts glowing.
The walls of the approximately rectangular chamber are lined with shelves, and the shelves are lined with nearly identical boxes. One of the shelves on the far wall has fallen, spilling its boxes across the floor; there are round balls of what looks like colored glass scattered across the floor at that end of the room, glittering strangely in Tias's light.
"That's the stuff," he says, crossing the floor to pick up a red-orange sphere.
It catches fire.
"Ow!" he says, laughing. "Maybe the weird thing they are is 'magic'? And, uh, don't touch them, I guess." But he has yet to let go of the burning orb.
"Maybe! See anything that looks like a book?"
He tosses the orb in the air and catches it. After the initial surprise, the flames don't seem to affect him.
The only thing in this room is shelves and shelves of boxes presumably containing magic balls, but there are two more doorways besides the one they came in; one even has the remains of a door next to it, or at least that's a pretty good explanation for that haphazard scatter of splintered boards.
"You seem like you'll weather failure at finding books that comes with success at finding... booby traps... better than I will." He cranes his neck but avoids tromping around; he might fall.
"Fair enough."
He sets the spilled box upright, puts the flaming ball in it (it goes out), waves a hand vaguely at the ceiling (it starts glowing), and wanders off down the nearest tunnel.
"You sure have a lot of random magical powers. Did you have any of them besides the possibility of sprouting wings before?"
"Nope!" comes the cheerful reply, from out of sight down the tunnel; and a few seconds later, "Ooh, skeletons!"
Giggle. Faint rummaging noises.
"It's your lucky day, the skeletons have books! Well. Had."
He comes back down the tunnel carrying an armful of books titled in an unrecognizable alphabet.
"Can you read those? Because I can't, and you're the one who mysteriously picked up my language."
"I can! There's a couple of what looks like magic textbooks and then I dunno what the other one is."
"Mm..."
The stone floor sprouts a stone table so he can put two of the books down on it and open the third.
"Some guy's journal." He flips to the end. "'We can hear the fiends scratching at the door every night', wow, ominous much?"
"Very, and I perform a sort of magic that involves me chanting about fire and blood and destruction all the time."
He giggles.
"Okay..."
He spends a minute or so flipping through the journal, skimming the entries that catch his eye.
"...So, this guy's on a research project in the middle of nowhere, he complains a lot about how boring it is, he's got a crush on one of his coworkers - she sounds hot, I wonder if one of the skeletons was hers - and then the weather gets all fucked up, like, 'the last rainfall recorded on the continent was three months ago', and so now everybody's trying to figure that out... then there's fiends, and the research people hide away in their little mountain hidey hole and bar the door and spend what looks like another month or two getting really sick of each other, and then the last entry's about the fiends and I guess they got in because those skeletons were pretty fucked up."
"Could be. I don't see fiend skeletons, but maybe fiends don't have skeletons, or there weren't any in the places we've been before they starved."