I really think any use of human sacrifice in LI should be entirely based on examples in the LI timeline as the basis for inclusion - Zalmoxians leap onto the spears, Emperor-sacrifice by the Sarmato-Brythonic Christo-Zalmoxians, etc. There are a wide variety of prisoner sacrifice, abdication/suicide/into-the-desert, death of courtiers/companions upon ruler death, and so forth in the LI histories written by Shaytana to allow for this without relying on pseudo-historical speculation on what "real Druids" or "real Norse" would have done. There is such limited information on the real world occurrence of such events that I can't state strongly enough how opposed I am to their inclusion in LI (Not, of course, that I have any real influence! I just figured I'd put my opinion out there, and I'll just mod out what I don't want for myself, which is what I do anyways!)
@ Ezumiyr
There is essentially no evidence of anything that Caesar claimed about the Gauls with regards to human sacrifice - to begin with, the limited evidence we have of human remains can easily be tied to any number of causes, including, but not limited to, execution of criminals, murder of politically inconvenient people, physical mutilation after death for the humiliation of the deceased, physical mutilation for glorification/memorialization of the deceased, etc.
The fact that there are bone remains in various states of dismemberment or mutilation, or that they are present near a holy or sacred site, emphatically does not mean that we can at all conclude that the remains were as a result of religious sacrifice. Are the Capuchin monks at Santa Maria della Concezione dei Cappuccini engaged in human sacrifice? They've got thousands of dismembered and reorganized bones covering an entire crypt right beneath a church! Clearly, this is evidence of human sacrifice..... except that it's not. Not to mention the fact none of the Aedui or Arverni, nor any of the politically prominent individuals of Caesar's time (such as, say, Vercingetorix), are at all tied to human sacrifice, even during the most extreme moments of the double circumvallation of Alesia. If there were any evidence of such actions, it would have been plastered left, right, and center. What's more, there is no evidence from later Roman administration of Celtic regions that there was ever any continuing practice of such sacrifices/worship, something that the Romans paid a lot of attention to and would most certainly have sought to root out. Certainly they opposed Isis worship, Christianity, Zoroastrianism, Mithraism, Dionysian/Bacchanalia worship, etc. There is simply no reason to believe that the Druidic regions had any real organized idea of human sacrifice.
Contrastingly, Phoenician (and later Carthaginian) first-born sacrifice, while likely exaggerated, certainly follows a known pattern of "first-fruits" sacrifice, and has a far greater deal of archaeological evidence than Druidic sacrifice. There are explicit pronouncements against such kinds of sacrifice and worship in the Torah from a period dating to before the founding of Carthage, and it likely had existed to some extent.
That being said, your idea of prisoner sacrifice and altered CBs are both not only good, but I think great. There is significant evidence of murder of captured leaders in war, and although in many cases this is explicitly NOT religious in nature, it could probably get a pass in the LI-verse, especially because Shaytana explicitly refers to it this way.
@ DarkReborn
-I would strongly suggest starting with prisoner sacrifice, which is pretty commonly mentioned by Shaytana's histories.
-I would pretty strongly oppose including the Slavic, West African, Celtic faiths in much more than that (there's evidence that the Slavs were WAY nicer to prisoners than most, in fact).
-I would say only very few religious would have infant sacrifice, and those would be Phoenician influenced specifically, not necessarily Canaanite in general.
-Courtiers and Wives/Concubines dying with the ruler should probably be a rather common thing - Norse, Egyptian, Solar, Tengrii, etc all have suggestions/evidence of such practices.
-Major Invasions or certain CBs probably could allow Graeco-roman sacrifice of courtiers for a piety hit and a boost to troop moral or something similar (It was an extreme, and not well regarded, practice, hence the piety hit, but might have been considered necessary and worthwhile)
-"Riding into the Desert" or self-sacrifice in various forms is well attested to in Shaytana's histories for the more established, Imperial level faiths, like Sol Invictus.
-The Zalmoxians have an explicit sacrifice of a soldier as a religious duty and an honor for the individual chosen, so that could definitely be included in a "Passover", "Lent", or "Hajj" like event chain.
-The Norse otherwise should possibly have blot events, but in all likelihood they would involve horse sacrifice, not human. But I haven't read through looking at Shaytana's implications for the Norse.
Basically, I think that sacrifice of prisoners is the best bet, followed by suicide style abdications and courtier/concubine/wife death upon succession. Otherwise, it's really really dubious. And I think our primary source shouldn't be what people "know" about actual history, but instead what is included in Shaytana's stories, so any time Shaytana's stuff conflicts with historical evidence or debates, Shaytana's should win, because alternate history. Which means if there is some clear evidence in the stories about the Slavs stabbing people for their gods, then more power to you! My two cents worth
Edits: Formatting to reduce the "wall of text" effect
