Bogomils were the Eastern cousins, and possibly ancestors of Cathars. They refused to use the cross and used a circle instead.
Valentinians were a very strange secret gnostic movement. They believed in a Demiurge and gnosis or secret knowledge required for salvation. Eutychianism was one of those high theological heresies, but was completely nonsensical. It's very complicated, and orthodoxwiki can explain it better than me. It was so ridiculous that Pope Leo the Great used it as a scapegoat to influence the Council of Chalcedon before the Great Schism. His letter to the Eastern Bishops opens with him cracking a joke about Eutyches' intelligence.
But what does that mean in terms of in-game mechanics (new or reused)? Bogomils just seem like the generic "Same as the orthodox religion but it doesn't have a religious head" Some of its core beliefs are impossible to implement without it being a bullet to the head of any poor soul that thinks it's a good idea to convert.
Quoting the Bogomilism wiki page
"Its followers refused to pay taxes, to work in serfdom, or to fight in conquering wars."
"Bogomils refused to fast on Mondays and Fridays, and they rejected monasticism."
"They declared Christ to be the Son of God only through grace like other prophets, and that the bread and wine of the eucharist were not physically transformed into flesh and blood; that the last judgement would be executed by God and not by Jesus; that the images and the cross were idols and the veneration of saints and relics idolatry."
It just seems like an extremely castrated form of Orthodoxy that's not worth using outside of an achievement run.
What I'm saying when I ask what sets them apart (And I imagine what Keizer Harm is saying as well) is what sets them apart
mechanically. Those heresies were pretty interesting to read about however I can't tell how they would fundamentally differ from Orthodoxy in-game. Both of them seem to have the issue that a solid 80% of the heresies do, they're just castrated forms of their parent religion.
There are some unique outliers like Fraticellism, Iconoclast, and Monophysitism that are nearly identical to their parent religion. There are the equality heresies like Catharism and it's downgraded cousin Bogomilism (I say downgraded because unlike Catharism it doesn't have access to absolute cognatic despite allowing female temple holders and no penalty to female rulers). And there's the meme heresy of Messalianism which has incest and no religious head to set it apart from Nestorianism. Those are the only ones I could think of that are different enough from their parent religion to bring up. Lollardy and Waldensianism are downgraded forms of their parent religion.
