So, my vote is for Slaynettes.
I think Belegar once said that the entire population of the Karaz Ankor could fit in Karaz-a-Karak itself?
Don't think we'll be seeing that change overly much in Mathilde's lifetime. If we want to fill holds, we're going to need to look outside of Dwarfs.
I like the idea of selling this to the dwarves as 'defense in depth'. The idea being that you have a central keep- the Karak- surrounded by a city built to be defensible and full of allied humans/halflings/(ogres?), with an outer wall that takes the brunt of any impact.
I think it's workable, if you think on a grand enough scale. It would involve, well, think of the Karak as the center hex on a hexgrid, and fortify/terrace for farmland the surrounding six hexes. The dwarves don't lose any space and can retain all rights to the human territory below where rock starts, plus they get to design and build very clever fortifications over a very large area that are designed to do two things: protect the humans from evil things, and protect the dwarves from there humans.
It's a great project that doesn't involve shedding dwarf blood and is likely entirely feasible for all the holds accessible from the border princedoms.
Oh! And set it up cleverly- the Dwarf King owns the Karak and the rock under it all, the Princes who swear are granted the soil in roughly a hex, so each dwarf king ends up with a council of six human princes that he can play off one another and keep mostly deadlocked, ineffective, managed, out of his beard, however you want to phrase it. Probably lay out a basic dwarf-law that the princes would swear to uphold and then demarcate their areas of authority.
K8P is going to be more integrated than that, but I think here is special. The other holds are not likely to accept this model as something to be changed to, rather than starting out this way, but I think a castle/city/outside variety of it would make sense to everyone.
But what if we make a spell that lets us teleport armies vast distances... by turning them into fog! Surely this will work perfectly! I am a genius!
I mean, turning that beast of a spell as High Battlemagic instead of cataclysmic magic would be quite a Trump Card. Situational, but if you absolutely need to get reinforcements somewhere ASAP...
So, here's my thought on this- we've got a ritual to work from, so we'll probably want to keep this a ritual. The main issues are the way supporting wizards attrite off with elements of the army as they fall their individual checks, the casting stamina required, and the skill of the primary caster.
I think we should keep it a ritual, but try and refine it. Set it up for two primary casters, using windherder to be able to separate the castings but combine the effects, and figure it like this:
One grey magister and one light magister with a choir backing him up. Each of the choir holds a light up, and soldiers cluster around them. The lights are a beacon for the soldiers to follow, a bubble of hysh to weaken reality around them, and a border where the shadows take over and provides a boundary where ulgu can gather. The grey runs through a modified version of the doomed march ritual, using the shadows around the army to pull in ulgu and swallow them whole in fog.
The choirmaster's role is to balance the power across the choir so nobody fails an individual check, the choir's role is to provide most of the power to keep the army out of reality, and the grey's role is starting, ending, and navigating the ritual, handling the arrival and departure points.
Basically, lean in the direction of a bubble of hysh floating along a river of ulgu between two points in reality.
I don't think we could make it a battle magic spell, but I do think we can make it a heck of a lot more practical for the empire.
Re: uncountable numbers spell-
This seems strictly worse than "a fog that allies can see through but enemies can't".
I feel like the selective visibility fog is probably going to take the form of a smoke screen type thing rather than covering the full volume of an army- 90% of the effects for 10% of the magical power, assuming power scales linearly with volume.
Uncountibility seems more like a spell you attach to a unit, as more of a fire and forget?
I like a large toolbox, basically.
I think the question about reclaiming dwarfholds is whether their surviving royal clans are prepared to follow Belegar's precedent and have the great majority of their Karak's population be human with them being a small ruling class.
Curious what you think about the model I laid out above.
I mean... this doesn't seem any less reasonable than Acid Fog? I imagine it'd just be another damage-in-this-area effect with a fog theme, or a save-or-die like Pit of Shades. In the latter case, we'd be trading "Fog-related" for "not having to invent the spell ourselves", and any balancing that needs doing would be trivially managed by changing the size of the area affected.
Also, we could call it Vaporise.
I like it! But it really is the same as acid fog: break down burning shadows to thaumatological equations, grab the part where ulgu eats into them, put that into a carrier spell that uses fog rather than shadow, and get a fog bank where anything that enters slowly sublimates away.
Oh! And if we call it Evaporative Fog, the command for use could be "EF them! EF those guys in particular!"