[quote=@Queen Raidne]
[@Willy Vereb] ...you gave me its actual material properties? <3 <3 <3 :wub[sup]†[/sup]   *breaks out her materials science book*
Anyway, yes. They're in. You've put thought into them; they aren't game-breaking; they have disadvantages and advantages; yes. Just yes. 
[sup]†That's the first smiley I've ever used on this site.[/sup]
[/quote]Wow, didn't expect such a warm welcome for them, I'm honored.
As for further specifics I'm going to claim some part of South America. I have yet to draw the map so I can't say exactly how much. The Heavenly Empire of Yllendthyr in the other game was larger than the USA but I'm not necessarily replicating this as a whole. Regardless it's going to be a big empire.

Technology-wise, the lightweight and durable mithril would give me some edge in speed for various technologies, most notably aircraft.
On the other hand Mithril is less stiff so it cannot control as much overpressure as with steel so they compensate with larger diameter shells and such.
99mm diameter would be only slightly stronger than a 75-76mm cannons from other nations, for example. Albeit the extra capacity for explosives will be welcome.
Engines-wise the elven noses can't bear the putrid smell of gasoline and other crude oil derived methods and instead they rely on bio-diesel and biogas and bio-kerosene. Technically the methods to produce all these were present. This doesn't exactly make them free of crude oil or coals but they prefer to only use these at large scale like factories and where it's inevitable, preferably while hiring only human workers.
Also because elven ears hate the noise of rapidly spinning propellers thus they urged to develop turbofans sooner. This means elven military aircraft (where the pitch of the propeller noise is the worst) use turbjets and turbofans. Jet aircraft may allow somewhat better speed but propeller craft in general are more fit to the military's needs during this period.
Oh, and in search for better airstrike methods the elves use flying bombs akin to the V-1 in combat. They sacrifice cost and number of bombs in return for the promises of more precise hits. They even trained aircraft pilots to act as FOs for directing the attacks.
It's a novel idea for bombardment but I think when faced with an actual war the elves may reconsider this method.
Same with their lack of heavy bombers.

Generally, military-wise they use several doctrines which is either outdated or too experimental because in the timeline of Yllendthyr WW1 never happened. They fought some proxy wars on colonies and some territorial disputes against other nations but that's it.
I leave the rest about Yllendthyr a surprise for now. I just mentioned the most risky parts in terms of balance.

[quote=@Mihndar]
I'd also like to volunteer for co-GM, since I have a fair bit of experience doing that (three years) and a pretty comprehensive knowledge of history, though Willy will probably still run rings around me in science.
[/quote]Sure, count on me whenever you need.
Used to research a lot on war history as a hobby but that was nearly a decade ago by now.
I'm not certain on my Ww2 knowledge but when it comes to the technicalities like what can a contemporary artillery do or how they found their targets, I'm here.
I can also aid people in terms of "What if?" kind of technological solutions.
What if you create a jet fighter in the late 30s? I can tell you that for example.