"...Are all of those using the same incantation? They would be very different spell structures in my world, to alter appearance versus function, and I do not think that the gills option is possible in temporary form at all." And he's curious to see what the incantantion is. Paper is ready. "I am ready to observe when you are ready to cast." 

"No, it's a set of three, the human one is one incantation and also the gills are different from the horns and stuff. Maybe because they're the most anatomically fiddly. Check this out, I can turn into you." Gesture gesture "Alter my form within the bounds of human flesh." Now he's an exact duplicate of Leareth. "It even does voices!" He adds, in Leareth's voice.

That is extremely useful. "You can do perfect illusions with no additional concentration," Leareth says. "Incredibly powerful. Hmm. Does it also, for example, give you the same weight and physical strength of your target? Can you change it midway without re-casting the spell entirely? How long does it last before requiring renewal?" 

"Weight yes, physical strength . . . I think so? But not coordination, if I tried to play sports in a differently shaped body I'd still be lousy at it even if I was copying an athlete. And I can switch it up but it has to go via my real form--like this." He returns to his normal self for a moment, then acquires bright blue hair and green eyes and an extra six inches of height. "And it lasts an hour unless I get too distracted by something."

“Interesting. We ought perhaps experiment at some point with how distracted is ‘too distracted’ and whether your focus on it can improve with practice. Certain situations are likely to be distracting.” He frowns. “Can you become an animal this way, and if so, do you acquire their abilities such as a bird’s flights?”

"No, unfortunately I have to stay basically human. I tried copying a cat's eyes one time to see better in the dark but it didn't work. But I do think concentration gets better with practice; I'm better at holding a spell while I do other things than I was when I started out a few months ago."

"But gills and breathing underwater does work? Is that some kind of special exception?" 

"Apparently? Maybe the incantation will make it clear. This one actually doesn't have a visualization component; it looks the same every time." He reverts to his usual self and demonstrates; the incantation turns out to be "Make my body suited to breath and speed in water as on land." Slits open on his neck, and his hands acquire webbing between the fingers.

Why that gets counted as the same spell, Leareth can’t fathom, but it’s not actually any weirder than Prestidigitation, and he supposed an access-point for mortals to use magic set up by a capricious demon might well be odd from his perspective.

“I suppose you cannot really demonstrate its function here,” he says. “And the third?”

The third incantation is simply "Grow natural weapons from my body," and it gets him a pair of ram's horns that look, frankly, stupid. Think "pair of cinnamon buns glued to his head" except he's not as good as Princess Leia at making them look reasonable.

Leareth smirks slightly, and makes another note. "I see." He's not clear that said horns are an especially useful weapon, but keeps that to himself. "I am ready to show you scrying now," he offers. 

"Yeah, I still don't really see the point of that third one," he says, ditching the bun-horns. "I don't want fangs or spines or claws or whatever. Let's check out scrying, that's way cooler."

Leareth sets down his papers. "I would normally use a focus of some kind for this," he admits, "and it will be more difficult and tiring without, but not to an infeasible extent." Most mages wouldn't be able to cast at all without a focus. Leareth, of course, has figured out a way centuries ago. 

He closes his eyes and raises his hands, and over about a minute, a flat circle of pearly light appears in the air. Then, quite suddenly, it flips to show a slightly-distorted view of Bruce's bedroom, seen from the perspective of a point hovering above his bed. 

Leareth grunts slightly, feeding more power into the spell. "There. I am curious if Nondetection might also block this one – can you cast it at a distance, on your bedroom as a whole? Shield is another candidate for a spell that might block it, though it could also be a purely physical shield." 

"Ooooh." Bruce walks around the scry, looking at the image from all sides to see if it has a back and if things seen through it exhibit parallax relative to each other. "What would you normally use as a focus? Can you scry places you haven't been? What happens if you pick somewhere dark, or a viewpoint that's inside an object or underwater? I can only do Nondetection on myself, sorry. Is there a range limit? Could you get around the range limit by scrying someone who was scrying somewhere else?"

Leareth gives Bruce a chance to have a good look (the spell looks like a fogged mirror from behind, from the front it's more like a flat TV screen than a window), then drops the spell; he can't hold it and focus on answering so many questions at the same time. 

"We use crystals, usually," he says. "Often with some of the initial spell-elements permanently cast into the substance of it – that is the main advantage of a focus. I cannot scry places I have never been unless I also have some kind of anchor there, for example, a matching focus-crystal or another object with a magical signature I can search for." The latter is a rare technique; Leareth wasn't technically the one to invent it, but the inventor lived and died in an obscure kingdom a thousand years ago and he may be one of the only people alive who knows it.

"If I select a location that is dark," he adds, "I cannot see anything unless it is also at close enough range that I can cast a mage-light there, using the scrying-point to aim. My range for that is in the vicinity of a mile. Inside an object, I have not tried, but I assume one sees nothing. Underwater is possible, but flowing water erodes magic in my world, so it becomes difficult to hold the spell at a constant point and it is much more draining." 

He stops to think for a moment. "Range is determined by the mage's power – it is more tiring to cast at longer range, both at the initial casting and to maintain it. I myself can manage a range of about fifty miles unaided, several hundred with a focus, and up to a thousand if I have assistant mages who can feed energy to my reserves." He smiles slightly. "I have not tried scrying another mage scrying, but it is a clever idea." 

"That's neat. Scrying your home world probably won't work, if range matters. Does any crystal work equally well? I can probably find you some quartz if it doesn't have to be anything fancy. Do you know why flowing water erodes magic?"

"I did assume scrying my home world would not work." He frowns. "Quartz is commonly used, as one of the more neutral options, so yes, that would be very helpful. Mages tend to have personal focus-stones as well, of more specific substances that they can work well with." He tugs open the neck of his tunic and pulls out a small chunk of amber hung from a leather thong. "This is mine. I have not needed to use it so far, since it is mainly for drawing in large quantities of turbulent or impure magic from outside oneself."

He tries to remember Bruce's other question. "Right. In my world, magic interacts to an extent with the physical world, and can be eroded in a way analogous to physical substances. Strong winds have a similar but weaker effect. Rapidly moving earth would likely do the same, but this rarely comes up." 

"Huh. That makes more sense than it just being water." He jots down a note to look for quartz, in the driveway gravel first and then at the store if that doesn't turn anything up. "If I go over there," he points at the other side of the basement, "and cast Nondetection again, can you try scrying me?"

Leareth turns to face the other way, and casts the initial step again. (If he has to do much more of this he's going to need to eat a few Mage Hands to recover.) 

"Interesting," he notes. "I...appear to be able to scry the basement itself...but you are not visible." He turns around just to check that he can see Bruce with his regular eyes. "Fascinating." 

"So it's like I'm invisible? Cool. What happens if I . . . ?" He picks up the cardboard box of Christmas decorations.

Now the box is also invisible! Leareth reports this to Bruce, and then apologizes and drops the spell before he hits the point of unreasonable exhaustion.

"I suspect that my magic is generally less efficient in your world," he confesses. "This spell ought not be as tiring as it is, and yet." 

"It does seem that way. Though now that I think about it I have no sense of how much power I'm actually using. I could just run out at some point. Zygynzaxx didn't say anything about that but he's a demon, he might have thought it was funny not to mention it."

Leareth thinks for a while. 

"Since it appears to me that you are clearly drawing on power from elsewhere," he says finally, "and since my best guess is that the reservoir is another plane and not a cordoned-off area within it, I doubt that." A thin smile. "Although, if you did, and if I am correct that the reservoir of power is Hell, that might be a very good thing for our mission." 

He has a brief and absurd mental image of a city full of demons having a power outage. "That's reassuring. Is that possible in your world, cordoning off an area so the ambient magic in it is separate from everywhere else?"

"...Not easily. With a specific technique, something similar can be done – power is keyed to particular mages, so that only they can make use of it. This technique requires the direct help of a god, however."