Kael, my second post ever on the forums. Congratulations on a really fun and interesting mod.
I had a few issues in my first game that I wanted to make you aware of.
1) Gypsy wagons in coastal cities can be attacked and destroyed by ships. I was playing as the Balseraphs and sent gypsy wagons to opponents' cities. My wagons in coastal cities were attacked and destroyed by pirates and, when I was at war, by enemy frigates. I didn't see naval units destroying any other land-based units, so I assume this is a bug, unless you intended to make gypsy wagons vulnerable in this way, although I can't see why you would.
2) I think others have pointed out that the AI doesn't seem to play the Infernals very well. I founded the Ashen Veil and brought the Infernals into the world. There was nowhere for them to settle, so they proceeded to declare war on everyone on my continent (the Lanun, Khazad, Grigor, and Svartalfar) except me, and were ultimately destroyed without having captured a single city. Maybe they should be programmed to attack the weakest non-evil civ, and go for the least defended city, so they can have a starting base? Just a thought.
3) While the Infernals were around, when I lost units in battle I got the message that my units had gone to serve the Infernals in the afterlife, which I expected. The problem was that after the Infernals were destroyed, when I lost units in battle I got a message that my units had gone to serve the Mercurians in the afterlife. My understanding from the "Fire" developer diary was that only units of good alignment would go to serve the Mercurians after being killed, not evil units. Otherwise, I think it unbalances things too much: I noticed on the power graph that the Mercurians increased significantly after the Infernals were destroyed.
That's it. Again, congrats on a great mod.