The first is that a pre-existing entity moves into the syncretic form, perhaps a numen or local wight who then gets a boost in popularity. Take Serapis, for instance: if He’s a 3rd century Ptolemaic creation to unify Greeks and Egyptians, He may have originally been a local spirit from the delta of the Nile. And the reason why I assume He’s real is that there are modern worshippers who claim Him to exist and interact with Him, which is enough for me, since I generally don’t deny the existence of a deity (see here). So you have a newly created godly form, joining Hellenic and Kemetic elements, that attracts a native entity, itself probably already aware of the presence of inhabitants from two different cultural backgrounds.
But what if a new deity is generated by the syncretic form? Yes, I know what I’m suggesting may come across as extreme, but not being a god myself and having no direct knowledge of Their deepest and most intimate life, I like to keep the options open. And an inevitable possibility to consider when dealing with new cult forms is whether or not it refers to a new deity altogether. In the myths, the relationships between the Gods are often told of in terms of father, mother, brother, son, and daughter, which may not necessarily mean They actually breed like us, but there is a generative notion. So what if to a syncretic form created and worshipped by humans, the Gods – namely Those that are combined in the new guise – reply by generating a new entity? Controversial as this may be, it’s still an option I like to keep on the table. And it’s perhaps worth noting that the Gods and Their realms may well be two very different things: Poseidon was given rule over the sea, but He didn’t create it; Hermes presides over lesser form of divination, but didn’t invent them. It’s not such a far-fetched possibility that a new god may be given a role already played by other gods with Whom He will then have to share it.
A third and final possibility is that of a new guise to an already worshipped deity. For instance, it seems the Sumerian god Enki was also called Serapsi, which is pretty close to Serapis. Could They be the same entity? Has the old god from the land of the two rivers taken a new form in the kingdom of the Nile after the death of Alexander in Babylon?
These are all possibilities, speculative answers to a theological question. They are not certainties or dogmas, not even UPG (at least not fully). And there’s one last matter to consider on the nature of syncretised deities, namely two types of syncretism: ontological and functional. More on that in the final post of this series.