A delicate flower of frost grows around the diamond for a moment, before evaporating into the warm dungeon air.

"I just pulled the carbon from the air, the same way I pulled the pebble from the wall," he explains. He grabs the diamond in his attention, and floats it in the air, turning it over.

"It's not very much. I'm not sure whether I could scale that up to a reasonable size. I bet I could do better with some wood or coal to start with, or something like that."

Kose stares at him for a moment, saying nothing.

Eventually she shakes her head. "It's fine. Just ... warn me next time you're about to do something like that, okay?"

"Of course. I didn't know it would be so dramatic," he reassures her.

"... right. So as I was saying -- you can pull materials out of the firmament. Not the air. It should feel like trying to pull something out of nowhere. One of my partners likened it to pulling a rabbit out of a hat, without the hat."

She puts the lightest emphasis on 'partners', in a way he might not notice if he isn't paying attention.

"So ... what is the firmament?" he questions.

Kose waves a hand vaguely at the air around them. "The fundamental stuff that permeates the universe. Some people call it the Ætheric medium?"

"Hmm," Yarold hums doubtfully.

He focuses his attention again, this time not on the air, but on the space between it. And then, before he can think about it too hard, he pulls a diamond out of it.

It's like being out of breath, or like giving blood. The vitality he had, the energy that he used to claim his corridor, bleeds out into the shape of a thumb-sized diamond, which falls to the floor with a tinkle.

"Yes, like that!" Kose cheers, clapping her hands. "Well done."

He just tries to catch his metaphorical breath.

When he has recovered for a few minutes, he addresses her again.

"That sucked," he informs her.

"It gets easier with practice," she assures him. "And it also gets easier when you have more Adventurers challenging you to rebuild your strength."

Yarold silently decides that he is fabricating as few materials as possible out of firmament, and will get by just fine using existing atoms from the air and from the soil.

"So I had best get started luring them in," he concludes. "Let me go think about all this and populate my corridor."

She nods, and settles on the floor again to wait.

Alone with his thoughts for the first time since his sudden arrival, what Yarold wants is a notebook to scribble diagrams in.

He settles for using his fantastic new powers to amalgamate some pebbles into a sheet of stone buried in the wall of his corridor and scratching some notes into it.

This whole setup feels weird. Being a dungeon is fine -- although the powers are wonky -- but there's no way that things are exactly as Kose is presenting them. For one thing, she clearly doesn't actually understand what dungeons are doing, which is pretty suspicious for someone who claims to have worked with a bunch of them.

Although perhaps not all dungeons are from modern Earth? He could imagine a random historical peasant grabbed from before the industrial revolution describing things in terms of Æther.

Ultimately, he just doesn't have enough information.

He turns his thoughts to his corridor. He has three sources of information about what has happened to him: experimentation, Kose, and whatever information on the outside world he can get to walk in through his entrance.

He briefly considers whether he can build a camera obscura into one of the support pillars, and take an image of the outside better than his own limited awareness provides.

He glances at Kose, and decides to shelve that plan. If he looks like he's building out her suggested challenge, maybe he can pump her for more relevant information on the world outside.

He presses down on the floor of part of the corridor, claiming the space and simultaneously compacting the dirt. He can't push it quite as far as he would like to, but he can still make a mildly annoying pit trap. Six feet deep and five feet across, suitable for bothering the unwary.

He grabs another stone and imagines a very flat monster.

It's either a mimic, or a self-opening trapdoor, depending on how you look at it. He imagines it fitting tightly over the opening of the pit, and then shrinking into itself when someone stands fully on it, or when directed.

He installs it, and then makes sure it won't close itself when one of his other monsters runs over it.

He places the slime right near the entryway to the corridor, and tells it to jump on adventurers and then retreat over the pit trap if it gets wounded. He also, after a moment of thought, scatters loose dirt over the pit trap hatch, so that it's not quite as visible against the otherwise-monotonous floor.

And then he pauses, to figure out what else he should add to the corridor.

He imagines a group of people walking in through the door. Imagines the slime jumping at them, imagines them slashing at it until it flees, and then pursuing it to finish it off.

He decides that what he need is a ranged option, to sit behind the pit, and harry the adventurers. He briefly considers whether he could put together a compound bow, but he hasn't exactly done much experimentation with materials, and he's not sure he could make something to string it with.

Eventually, he settles on a sling. He goes with a skeleton, because those are easy to picture, and equips it with a sling. He doesn't want to make more materials the hard way, so the sling is also a monster, one that will bite an unauthorized user if they pick it up. He gives the skeleton a pouch full of stones pulled from the wall, and sets it up on the other side of the pit trap, with orders to fall back to his main room and keep harrying the attackers from a distance.

The whole setup is fairly simple. He could add more monsters, but he's not well-calibrated on how much force is reasonable here. He plays through his imagined invasion in his mind's eye again, trying to imagine how it will go, and any more complications he can add.

He's ideally looking for things that can have variable difficulty, so that he can adjust them to different circumstances on the fly.

He tells the pit trap monster to let the first person pass if there's a large group, to split them up. He carves holes in the wall for the slime to hide in, and then decides that's too obvious, so he changes the slime to have a rock on its head that it can use as a shield, or to close off the hole once it's hidden.

He fills all the holes with slimes, so that he can wake up a variable number as the fight progresses.

And then he realizes he's been having a failure of imagination.

He replaces the wooden tunnel supports with monsters. Monsters that will just sit there holding up the roof until he needs to trigger a collapse for some reason, at which point they will pull down the ceiling.

He floats the wood into his core room, and piles it up for later reprocessing. He's sure he can find a use for some good wood.

Kose starts as he brings in the wood.

"Did you remove the tunnel supports?" she asks, rushing to look down his corridor. She pauses, seeing all the supports where they used to be, and a single skeleton with a sling standing about half way down. It waves at her.

Yarold realizes that in his creative focus he failed to consider whether he wanted to keep knowledge of the tunnel support monsters to himself.

"I was just thinking about future expansions," he extemporizes. "It's easier to make matching stuff if you have something there to copy, and I'm expecting these tunnel supports to get scratched up once we start having fights in there."

She looks at him dubiously.

"Yes, well, Adventurers will be here sooner or later. You should probably focus on your one corridor for now, and then we can plan an expansion once we have more to work with."

Yarold is perfectly clear on who is doing the planning, here.

"Yes, certainly."

He looks back at the corridor with fresh eyes, and decides to add some visible slimes, and a second skeleton, this one equipped with a sword to defend the ranged skeleton as it falls back.

He tries to conduct another failure analysis -- imagining that this setup did fail, and trying to figure out why that might have happened -- but ultimately, he is still running pretty blind. He has no idea what adventurers will be like, whether they'll have physics-defying abilities of their own, what the consequences for failure even look like, how his monsters will respond to scenarios he hasn't pictured exactly, or anything like that.

He turns his attention back to Kose, finding her mumbling silently to herself and twisting one of her rings.