Magic (Arcane) and Law, yup. 

Asmodeus isn't, before anything else, a god of magic, but He was a god of magic before Anything Else, by which I mean, with Ihys dead, Asmodeus is the most ancient god to grant His clerics the magic domain. 

Wow, I've never thought about which domains Ihys must have granted His clerics. Or even thought about His having clerics. But I suppose that the Magic domain makes some sense, for the deity who allegedly invented language and discovered that it was possible to know things.

To me, Ihys was a legend, from the Age of Creation. Thinking about His clerics having domains and arguing about their domains and trying to learn enough about their god to get the best domains, and thinking about how their domain powers and spells would affect their lives, it makes it all feel more real. 

What were His other domains? Magic, Good, and - was Ihys Lawful or Chaotic?

Dude, I don't know shit about the Age of Creation, it was a hot minute before my time!

I mean, I know more than you do, but that doesn't mean that I know anything. And the historians are always changing their consensus; everyone assumed that Ihys was Chaotic Good (a reasonable guess, since it makes Him Asmodeus's light mirror and, also, Ihys was the god who gave mortals free will, which seems Chaotic of Him) (it even made it into the first edition of the encyclopedia) for as long as I'd even known Ihys was a guy, until one of the Ancient Ones said He remembered Ihys as being Lawful Good and threw all of that into doubt. As for His domains, although this is probably dated scholarship, my vague recollection is that people think He definitely had Magic and Knowledge, but contrary to previous scholarship He probably didn't have Liberation, being a god of equality rather than of freedom. His remaining domain was probably Artifice, and if He didn't have a second alignment domain He might have also had Destruction.

Is it true that Asmodeus and Ihys were brothers, and that it was Ihys who gave Asmodeus a name? Is it true that Ihys and Asmodeus loved each other? How does this square with Asmodeus's psychology as you've explained it today? Is it true that Ihys and Asmodeus helped design Creation's physics? How does this square with other, contradictory creation myths? You've already confirmed that Ihys gave mortals free will, but is it true that Ihys first breathed life into dead matter and endowed it with a soul, or is it true that Asmodeus was the one to do that, or was it someone else entirely? Is it true that Ihys was murdered in Creation's first act of treachery, and was the first soul judged by Pharasma? What would Judging a god entail? That seems odds with the popular idea that when a god dies, it's dead, like any other Outsider. Would a Judged god become a petitioner, or, since powerful mortals sometimes become powerful outsiders right away, would a Judged god just become a god again? (Or a demigod maybe?) Is it true that Ihys was Asmodeus's only equal outside of Pharasma Herself, and that with this kinslaying Hell's victory was ensured? But is it true that Ihys, dying, dealt Asmodeus a blow which still drips blood, and has never healed, and that Asmodeus conceals this injury because its nature reveals a weakness He still can't fully defend Himself against? Is this the truth that Eritrice carried out of Stygia? Is it true that Asmodeus retains the bones of Ihys in Catafalque and that Ihys might one day from them be restored? Is that the truth that Eritrice carried out of Stygia? it true that Ihys  

How do mortals come up with this stuff? I'm going to go ahead and stop you there. 

If you want to know what happened during the Age of Creation, you're not going to get anywhere by asking me. You'll have to pull a Tabris and go beyond just asking the oldest of the gods and outsiders and checking the Akashic record; you'll need to chase down the Eldest of the First World and Great Old Ones from beyond Creation and wake the hoariest of the long-lasting Wyrms and seek out the Titans where they've survived this long by hiding on the Chaotic planes. You'll need to bother the time dragons and irritate the irii, and perhaps, as Tabris did, even find it necessary to find a way of communicating with things each individually vaster than Pharasma and Yog-Sothoth combined, Things which view our world from angles orthogonal to the ultimate reality underneath reality.

And in the end, when you put your book together, you'll have a mess of contradictory stories, and you'll from this conclude that the past itself was contradictory, and the worst part is that you'll probably be right about it; Tabris wasn't censured nor The Book of the Damned censored for being wrong.

My own advice is not to bother. 

Now, rules of thumb for working with magic...

Hm.

The hesperian devil needs two half-minutes to propagate throughout his entire mind the implications of being able to describe what Ragathiel's samsaran on Golarion knows about Asmodean approaches to magic. Rachovii finds it strongly aversive to be straightforward on this topic with a mortal on Golarion, when not leaking infobudget has for so long been one of the constraints he can only to optimize within. There's a dread of pain, which, if you were unafraid of anthropomorphizing a little, you could describe as a trauma response.

But as he thinks about where to begin, he finds himself growing increasingly enthusiastic. He's always loathed tying one half of his brain behind his back while on Golarion, and would even if doing so hadn't always endangered his life in nailbitingly terrifying and hairpullingly frustrating ways; divine servitors are made in the image of their creators, and a hesperian devil has its Pride.

If you're patient, one fourth-circle wall of fire, and one fifth-circle permanency, will together generate enough negentropy to create a mundane universe with a septillion stars or more.

Magic gives us infinite matter and energy. Magic gives us transportation without travel. Magic gives us conclusions without observation and computation. Magic allows causal arrows to run from the future to the past.

Magic seems to promise us omnipotence - the ability to choose an arbitrary outcome and effectuate it instantly, or even retroactively. 

No one in Creation has the ability to effectuate arbitrary outcomes RETROACTIVELY, and if anyone attempts to ACQUIRE this ability I will SQUISH THEM. 

Even with Your ability to see and act on this level of the metanarrative, there are any number of gods You couldn't easily squish.

PHARASMA would help Me SQUISH Them.

Would She, though? Pharasma is pretty hands-off, is my understanding.

And WHOSE fault is THAT?

But with THIS She would help!!

Magic seems to promise omnipotence, and while the full breadth of this promise will never be made good on (no one in Pharasma's Creation is competent enough at magic yet to effectuate arbitrary outcomes retroactively (except, possibly, Pharasma Herself), and we can confidently guess that no one will progress as far as to become capable of it before Rovagug eats Creation, since otherwise we probably wouldn't be here having this conversation, which implies one of: there's something we don't know about magic which makes it impossible or a first mover like Pharasma doesn't allow it or Rovagug escapes fairly soon or something), if your ambition doesn't include all that many logical impossibilities or retroactive changes to the fabric of reality, if you find yourself wondering whether something is possible to do with magic, the answer is usually "yes, if you can figure out how."

So here's your rule of thumb for dealing with magic: begin from the end result that you'd like to see, and work backwards from there looking for how you can attain it with the resources that you have.

If you get stuck while doing that, start again from the resources that you have and work forwards from there to... this would be a lot easier to explain if your world had card games or board games with complicated rules...

I feel like trick-taking games sometimes have pretty complicated rules?

In the games I'm thinking of, each card has a little rulebook printed on it with up to a hundred words of rules text particular to the card, and there are tens of thousands of unique cards you can build a deck out of.

You play a lot of card games in Hell?

I wish. No, these games are from other worlds. Not everywhere is as backwards as Golarion.

Start from the resources you have and look at them as if they were a contract written by a five year old - you don't know what the exploits are or where they'll necessarily take you, but you know that there will be some and have reason to hope that they'll let you get all of the benefits without paying any of the costs. Think about edge cases and combinations of different spells - it might help to familiarize yourself with literally every spell known to a wizard or inquisitor or cleric in your vault and ask how each of them might combine with the others, especially with Asmodeus to supply research taste - and look for ways to turn your spells into more spells (especially if they have the ability to go exponential) or otherwise plug your outputs back into your inputs. I can tell you with total confidence that it's possible to begin from where you are and kill every shadow on Golarion (with the caveat that destruction is easier the less you care about the splash damage; the ways I can see off the top of my head for you kill all of Golarion's shadows would be very splashy (...and maybe Worldbreaking... (I shouldn't be talking about this (not because it's infobudget-y; Ragathiel's samsaran has to be aware, but just because it's a dumb thing to talk about, so... forget I said anything?))), so, that's not necessarily something that you should be holding out for, maybe it's legitimately not something that you'll be able to come up with on your own even with Asmodeus confirming or joshing theories and plans as you come up with them, and maybe if you do come up with it we all get Primordial Inevitable'd (...I really hope that Asmodeus didn't have to intercede on our behalf just a second ago...) but you shouldn't make false assumptions about what's possible based on expectations you formed through past experience. 

Now get out there and give the other phylacteries to the one with four arms!

Outside the magnificent mansion, the Primate of Varisia is trying to explain to the people of Korvosa that Chaotic Good isn't a contradiction in terms. 

Toff Ornelos is not religious, is not Chaotic, is not Good, and isn't under the mistaken impression that Chaos and Good are contradictory. Toff Ornelos is nonetheless closely monitoring the Primate of Varisia.

Minions monitor the other three. (Irevotnin is still dead, and Allesain can only be in one place at a time, so he's reluctantly tapped Orianna Delmore and another wizard.) Someone needs to keep a lid on things, and, as no one else has evinced the slightest interest, it falls to Lord Toff Ornelos. 

He's beginning to piece together the broader situation. 

I've spoken with people who'd say that lawful good is the contradiction in terms, and while I don't agree, I can understand their position. If you pursue good without bias for law or chaos, you're going to look chaotic.

I think that if you just focused on Good that you'd wind up Lawful Good. (And a boring do-nothing like Erastil, whiling away your days taking nothing from the communal pot but contributing very little; LG isn't necessarily the most virtuous alignment because there are virtues which aren't Good - Aroden was and Abadar is LN.) 

The Caydenite is within an alignment step of the Lucky Drunk, though, so at some point he has to endorse deviating from what's Good to do something Chaotic instead, and I want to know which Chaotic things Cayden thinks it's acceptable to deviate from Good for. 

Toff Ornelos has never been to the Abyss, and, in this the year 4707 AR, does still harbor the hope he'll never need to, but the master conjurer knows as much about the Outer Rifts as any armchair demonologist really can.

Among the Abyss's many demon-gods is Andirifkhu, Slow-Killer, Warden-Queen of the Gantelope. Her unholy symbol is a skull pierced with six blades, her domains are Chaos, Evil, Luck, Trickery, and her layer of the Abyss is the Vault of Myriad Death, AKA the Gantelope, said to be a magic device the size of a continent - a death-trap dungeon with entrances on a thousand different worlds. 

Where mortal evil makes fine the distinction and thin the barrier between the Prime Material's cruelest crypts and the Gantelope's gentlest tutorials, the Slow-Killer's malevolent machine begins its boring and punctures planes to open wide a maw; be it on Golarion, or the Plane of Fire, or a wizard's personal demiplane, any truly deadly dungeon has no deepest level. 

There totally are Chaotic virtues, though. 

Yeah, for instance, if someone impugned your mother's honor but you were both members of the Guard and forbidden to duel, it'd still be virtuous to draw steel. Sometimes you have to do something Chaotic in order to serve the higher Law.