Children of Perun is an obvious choice for reformed Slavic religion because it's a unique doctrine only Slavic religion can unlock. The rest is dependant on what you choose to focus on. Unyiedling nature is a valid choice because Slavic pagans were "defensive" pagans before Holy Fury came out. So it's basically allowing them to keep the defensive bonuses that came with it. Plus, with missionnary work coming from Abrahmic religions as well as potential wars against them and/or other faiths, it's likely Slavic reforming their religion people would be resilient to conversion. So in terms of roleplay, it could make sense for Slavicism to reform that way. There are two other Natures that I could consider for Reformed Slavicism, based on the description of Children of Perun. It reads All of the Children of Perun will come together, sharing a new, harmonious understanding of the gods, so that we can live in peace and prosperity with our neighbors. Since the text insists on harmony, peace and prosperity, taking Peaceful nature could make sense. The other alternative would be Cosmopolitan because of the "new understanding of the gods" part as well as the fact they mention neighbors: the Slavic faith could thus reform in a way that would be more open. In terms of the second doctrine, Ancestor Veneration seems like a very solid choice. One of the bonuses Slavicism keeps on Reformation is the Ancestor Worship ability, the event where you make a sacrifice (A body part, a prisonner/courtier, gold or a carved idol) for your ancestors in exchange for a bonus. From a thematic perspective, Ancestor Worship takes things to the next level as you would have cults for worthy Ancestors showing up. That said, it depends on whether or not Ancestor Worship already translate into Ancestor Veneration upon Reformation. From my understanding it doesn't, so you don't need to fear redundancy. Plus I have a bit of a hard time seeing another good alternative doctrine to pick. In terms of leadership... Well, given that you've picked Ancestor Veneration, this unlocks the Eldership succession doctrine. Eldership has your ruler elected by the six oldest living members of your court. And generally speaking, Elders kinda occupied a religious function... So you could make the argument there is a separate clergy already existing and that they have their own mechanism for choosing their leader. Thus Hierocratic is a logical choice to pick. That being said, Children of Perun also give the same boost as stability does. And stability's description itself seems to insist on the fact that what matters is that Kings are chosen by the gods so they should be respected as such. Plus it does get rid of the short reign penalty. So I feel Temporal probably could work too. On a side note... Is it just me, or does it feel like Autocephalous is the least attractive choice among the leadership choices you can pick on Reformation? Temporal has obvious gamey advantage, but you can also choose it to pick it for roleplay if you feel Temporal and Spiritual authority could be mixed (or want to play a God-Emperor). Hierocratic seems like the most logical choice because you're likely to unify your religious practices, thus you'd need a unified leadership. Autonomous basically fits if you want to play open-minded religions, especially if you've decided to go for Cosmopolitan nature and Syncretism. But Autocephaly? It's a bit of halfway point between Hierocratic (unified practices) and Autonomous (no unified leadership as it's collegial) and thus suffers from that fact.