[cthulhu]

I'm not sure about what happened. In theory, your prophet might have sneaked somewhere where you didn't look, but IIRC he should still be shown to spread dominion in the Temple screen.

My best guess is that I accidentally removed his goblet and he drowned.

There are at least two possibilities:
1) It might be that didn't have any commanders capable of leading magical units any more. Was you Niefel Jarl feeble-minded?
2) To stop never-ending battles (e.g. a Sphinx against creatures it can't kill with spells), all attacking units auto-rout at turn 50. Berserking units could stay and fight even after this. I don't remember whether the defenders are supposed to rout before or after any remaining units are killed, but it might be a case of a berserk Jarl fighting longer than the battles are supposed to last.

I doubt it is a bug, although it isn't as clear as it could be.

Yeah, it was about 50 turns before the VOs started spontaneously dieing. Doesn't really seem like the most wonderful mechanic in the game. I mean, when an SC goes up against a large army, and kills 2 people every turn, and eventually arbitrarily dies because the battle has gone on too long, well, the SCs owner is not happy! That one was kind of expendable but I had another with 30+ each in protection, defense, and magic resistance that I would have just curled up into a ball and cried if that happened to him.

The Vampires couldn't rout anywhere, so they died. Units can only retreat to friendly, neighbouring provinces. Even fliers, sneakers, etc follow the same rules. It seems that immortals killed by retreat aren't reborn; that might be a bug.

I think usually when my vampires die due to "fleeing into hostile territory" they respawn in my capital (assuming the battle occured in friendly dominion).

You quessed it: Communion Slaves are supposed to do nothing for the rest of the battle, but a bug may cause them to act strangely.

Blerg. It would be nice if the spell description mentioned that it paralyzed everyone who casts it. Now I'll have to figure out how to set it up so that the slaves form a protective wall around the masters. The masters will end up needing protection from arrows and area effect spells. Sigh.

Not a bug per se, but there are oddities in how Lycanthropos' Amulet changes creatures (including Jotun giants) into werewolves. There are bigger werewolves in Dominions 3 (EA Niefelheim has Jotun Skinshifters), so it might be partly fixed, but even then weird things will happen. There should probably be some types of units that are immune to the transformation, and inanimate beings and/or magical beasts (I'm not sure what Ivy Kings were in Dom2) probably shouldn't change.

Blerg.

The first might be a bug, or just an oddity in the order in which battles and dominion spreading happens. E.g. events might affect it. Dominion spread happens after all battles, so an event might change the province into hostile dominion before battle, and normal dominion spread could change it back after the battle happened but before the hosting was complete.
Not sure of the second.

The first is extremely annoying when playing a vampire queen, and contradicts some dev quotes around here somewhere IIRC. The second appears to be an obscure bug, but I didn't test it after the first time so it could easily just be a coincidence.