I'm on my fifth playthrough of the game, 597 hours in total. The first four playthroughs were as various Pagan and Muslim faiths. I never once saw anything about a heresy appear in game.
This time around I decided to start as a Catholic and establish a new Christian faith. I've already been given two separate prompts asking me if I want to convert to the Cathar heresy, and then later my new Christian faith was declared a heresy and about six random rulers throughout Europe decided to convert to my faith without any input from me.
Seems like heresies are a big deal when you start as a European Catholic but I had no idea they even existed before this. I tried reading up on it and it seems like heresies occur when Fervor is too low.
Does anyone know if heresies can occur in other religions? I usually don't pay close attention to Fervor, so I'm not sure if it's a Christian-exclusive mechanic, or if Catholicism just happens to be one of the only faiths with such a swingy Fervor score.
Disclaimer: I‘m no expert, if anyone‘s a pro on this, please listen to them.
AFAIK and IIRC, heresies can appear in any religion when the fervor drops low enough, at roundabout 50%. I vaguely remember getting heresies on my „Mother Of Us All“-playthrough in Africa (African faith) and Lingua Franca playthrough (Muslim faith), but it‘s been a while.
Fervor is pretty funky in the game cause winning holy wars, for instance, LOSES you fervor for some reason, so I guess the pope likes to nuke Christianity’s fervor which leads to lotsa heresies. There‘s a mod that „fixes“ that. Unless they changed how it works, I haven‘t kept up with patches.
Hope any of this helps. Again, I‘m no expert, just wanted to give you something to go by.
That makes sense. I'm curious to see what kind of heresies would appear for various Pagan or Eastern faiths.
From what I read, the Fervor threshold for heresies is 40%. I also saw a mod online that causes Fervor to gravitate toward a lower value, so that most faiths' Fervor doesn't stick at 90%-100% anymore. I'll have to look into it some more. Thanks!