More along the lines of the original purpose of this thread, I had a recent brainstorm: What if all of the Avatars (for this to work there would need to be one for each religion) spawned automatically at AC 70. Depending on the status of the holy city (mainly if it's in the wrong hands) they could start barbarian.
AV: Goes barbarian if the city is held by a non-evil civ.
RoK: Goes barbarian if the city is held by an evil civ.
New avatars:
Order: The angel that was opposite Sphener when he volunteered to fall. Goes barbarian if the city is held by a non-good civ, but is under AI control (like enraged) if it's a non-Order civ.
OO: Some form of tentacled monstrosity from the depths. Weaker than the other avatars, but has Water Walking and double strength in water tiles. Goes barbarian if the city is held by a non-OO civ.
CoE: A shadow avatar, weaker than the others but invisible and with hidden nationality. Only goes barbarian if the city is held by an Empyrean or Order civ.
Empyrean: The archangel of Lugus. Can cast all Sun and Empyrean spells, and has Sun affinity. Goes barbarian if the city is held by an evil civ.
FoL: No ideas yet.