To continue the mashup of ancient Norse mythology and the medieval Christian church, let’s talk about turning the undead.
I just ran an adventure in a setting where the undead were unknown. As far as I know, this is consistent with Norse mythology in the real world.
In the setting, there are vampire stories, but they’re just stories. Then a cleric of the Aesir met some walking corpses. The player of course moved to turn the undead, but the character would be pointing his silver Yggdrasil at the zombies as a measure of desperation, commanding the souls to leave the bodies (“The power of Thor compels you!”). And the undead halted, however temporarily. A crude attempt that was effective at that moment when emotions were high.
The undead in this temple long before the characters were born, long before Thor built a temple to Odin. So there would be no existing tradition of repelling the undead. Where might the cleric turn to improve his results? I think it likely that the cleric and party, should we continue this as a campaign, need to consult a shaman, who would be more attuned to using spiritual powers to ward off threats that are older.
Many times religious traditions have absorbed older ideas and characters. Perhaps a shaman’s god would be considered an aspect of an existing saint or being in the established church. Perhaps this would become a wrathful version of a saint or demigod, much as wrathful demons were held by Buddhists in Tibet to be wrathful forms of bodhisattvas.
This of course might be seen as heresy by the established church, putting the cleric at odds with his order…
Lot’s to work with there.