All right it probably doesn't take that long to get one spell and he doesn't have anyone else to cast it on him right now - he's mostly not using magic, he's here to coordinate, but obviously more backup is better. 

He Mindspeaks some mages to cover him, and also Mindspeaks Taver to let him know that he appears to have gotten more cleric powers and given how the gods work this probably means Asmodeus is up to something. And then he gets out his holy symbol and kneels and reaches for the now-familiar interface with Abadar. 

He can have Lesser Restoration! He can have three of it, if he wants.

He'll definitely take three of it! Leareth pushes a feeling of gratitude toward that now-familiar presence, which is still kind of terrifying but also its own flavour of reassuring. 

Affection, pride, confidence.

A devil steps out of the temple of Asmodeus and fills a hundred-foot-square area with LOTS AND LOTS OF FIRE.

Not that many of Leareth's soldiers and none of his mages are within that area, because Nayoki has been warning everyone to keep their distance while they figure out what Asmodeus is about to do. Farseers are watching, messages are hissed to Mindspeakers who inform Taver. 

Leareth relays to his mages, telling the nearby ones to swap to heat-sink shields; he's also not sure Velgarth magic is the best bet against this, can Taver ask some of Aroden's wizards for advice. 

One of Leareth's mages who's also a Farseer and comfortable with distance casting flings some levinbolts from apparently-nowhere at the devil, just to see if that does anything noticeable to it. 

It does something! Much less than it'd do to a person, but not nothing. 

The devil takes off in the air, flying towards the army.

Some more devils join it. 

The trembling cleric of Asmodeus stands up from praying for spells and asks Asmodeous to miraculously fix everyone in the temple who has been affected in some way by the invaders. Whatever it is that the invaders did. 

Asmodeus would be delighted. 

A couple hundred of Leareth's mages are in the city and fifty are within range. Levinbolts and concentrated spears of mage-energy and other more exotic attacks are flung at the devils by everyone who has line of sight to cast and a few who don't but can distance-cast anyway. 

They can throw lightning bolts at each other.

High Priestess Aspexia Rugatonn gets herself miraculously cured, scrambles to her feet, gives hurried orders to make sure the fight for the city is as costly as possible for the attackers, Plane Shifts to Hell. 

Not to that deepest level of Hell where Asmodeus is, of course, you can't get there with a Plane Shift and would be very unwise to go uninvited at all. But in the first level, Avernus, they'll at least be able to plan their response unimpeded, and their enemies seem quite competent to impede them in Cheliax itself, right now, somehow - how -

It is a question than an extraordinary number of devils and demigods in Hell have already been set to answering. They watch backwards in time through the last hours, weeks, months, years, they learn of another world and send their searching there, too -

- they are interrupted by an invasion of Hell from Heaven, because of course they are -

Leareth Mindspeaks Taver for an update on how the city is responding - the defending soldiers and clerics, but especially the local civilian populace. 

In addition to being able to Broadsend to thousands of people at once, Taver is an incredibly powerful Thoughtsenser, and most of the citizens don't have much in the way of shielding. He has to stop Mindspeaking to do it, but everyone's heard the message repeated quite a few times now, and he can divide his attention to reach across miles, skim a hundred people at once and then another hundred, consolidate an overall impression - how are people reacting? 

People are so incredibly terrified! They're terrified that this is a ploy of some kind to test their loyalty. They're terrified that it's a war between gods and they're all going to die. They're terrified that they're going to be killed for picking the wrong side, or for not picking a side fast enough. 

(They're hopeful - but it can't be true, and someone'll ask them, next week, maybe under a truth spell, did you desert your loyalties so easily, are you so worthless to Asmodeus, is there nothing of you that will remain when the unworthy bits have burned away -)

They cower in their homes and remind themselves that someday Asmodeus will conquer all the worlds, that people believe going to one of the nice afterlives is an escape but Asmodeus will come for them there, too, that hope has always been the enemy of good judgment. Some of them are thinking about which neighbors to accuse of disloyalty when Asmodeus wins, and as a backup plan which neighbors to accuse of disloyalty to the new regime if Asmodeus somehow loses.

Being upset about it right now won't help, so Leareth isn't, he folds that away for later. People cowering their homes is one of the best options, here - in some ways better than them joining the fight on Aroden's side, because that risks a lot of untrained civilians getting killed in crossfire. 

He asks Taver to switch his focus to the soldiers and lower-level casters, who won't be the focus of as much attention, and to start divvying them up into sections based on who is near which of Leareth's mages, and inform said mages that a particular contingency-order is now in effect and of who their assigned people are. Oh, and also to let Aroden know he's doing so, so things don't get tangled up. 

In between throwing attacks and shielding themselves, Leareth's mages find moments to reach out with compulsions - for those who don't have Thoughtsensing, Taver can help them anchor on the right minds. Casters first, then common soldiers. 

The compulsions that go out are subtle. They'll show up to enchantment sight still but hopefully most people are too busy to check. The soldiers and casters affected are just going to be missing and fumbling a lot more attacks than they would otherwise. 

Cheliax starts sending in forces from elsewhere in the country, only the ones that can Teleport for now. Asmodeus is being extremely generous in granting prayed-for Miracles and in sending more powerful and more cooperative devils than you'd ordinarily get from these planar binding rituals but not, so far, intervening farther than that. 

They need people who can do Gates. The obvious thing is to try to grab some, with Dominate Person or Geas spells - convince them to switch sides and be rewarded in this world and the next one -

Leareth and Aroden were expecting this, because it's kind of the obvious next step for Asmodeus. They tested the spells against Velgarth shielding, which can shield out any mage-compulsion, but apparently that's not the case here; it makes it more likely someone can throw off the spell, but doesn't render them immune.

With more lead time they could have figured out shielding, either a local magic item or purpose-built Velgarth spell, but as it is, the best he could manage was a voluntary compulsion on all his mages. They know what Dominate Person and Geas feel like; some had it cast directly on them as a test, others with Mindspeech rode along in their minds or observed the memory. The compulsion is a subtle, conditional one; all it says is that if they sense enemy mind control, they must immediately stop taking actions, and contact Leareth and Taver, either with Mindspeech or a communication spell or a one-time-use emergency talisman for those who can't manage either. 

How Leareth will respond to that is going to depend on the exact conditions, but having Taver to coordinate through gives them a lot of better options than they would otherwise have. 

Then when the spells land, rather than enemy mages jumping over to their side the enemy mages just stand there! It's still a decent way to take them out of the fight but this is an unusual and frustrating result and Cheliax's wizards are frustrated. 

Also they are running low on spells, though their opponents have to be running low on spells as well.

Someone Sends Aroden that Hell extends an invitation for him to visit and discuss terms and thereby avoid his obliteration in open war.

Leareth loses a few of his mages that way, when no one else is in range to cover them with a shield and buy time to grab them, which is very irritating. He yoinks a few by dint of opening very fast Gates right under them. Unfortunately, actually breaking enchantments is risky to do by the low-powered Velgarth method, and the spells to do so are limited, Leareth's other mages can refill spell slots for wizards but it's eventually tiring for them to cast more than their usual spell allotment. Mostly, though, they can hold their own, and his mages aren't running low on spells, they'll eventually get tired but they're well trained and there are nodes that no one else on either side is using as much. 

Aroden does not acknowledge the Sending in either way. 

Second contingency-order. If an enemy soldier is wounded, they get a compulsion to stop fighting and instead get out of the way, pretend to be dead and avoid notice from the enemy. Ideally one of the subtler ones, where it's not obviously distinct from their own desires, though not all of Leareth's mages are skilled enough for that. 

Leareth asks Taver to alert him directly when higher-level casters are wounded, because he's very good at subtle compulsions and also seems to be better at getting past the weird local equivalent to shields. 

High level casters with access to magic healing have very little margin between 'not injured enough to impair them in fighting' and 'dead or dying' but there are some. Their own side's clerics can use a spell to distinguish the injured from the dying or the dead, but, well, there aren't enough of their own side's clerics.

Someone orders a withdrawal from Egorian. 

Probably someone also ordered it torched because it sure is on fire now.

Fortunately Velgarth magic is really good for putting out fires, even at a relatively low power cost. Reverse weather-barriers go up, keeping the fires from getting hot enough to spread without otherwise being too obtrusive, then chilling them until the fire loses momentum and goes out as soon as the casters have withdrawn. 

Withdrawing forces from a city is never the most organized process and Leareth can take advantage of this, throwing compulsions at casters and then at as many soldiers as he can reach to get 'lost' and not make it out, or, if he thinks he can get away with it based on their thoughts, to be seized by sudden doubts and fears and decide they would rather be Aroden's prisoners than fight the rest of this war on Asmodeus' side. 

Some of them are in fact in enough doubt (it's not Aroden, it can't be Aroden, but whoever it is Asmodeus hasn't crushed them like a bug yet -) that the compulsion can drag them to a terrified surrender. - presumably he'll kill them and then they'll go to Hell and it'll be so so much worse for having ended like this -