When I wrote Gods & Demons, I referred to pantheons, but I really glossed over them. I figured everyone knew what a pantheon was, so we were OK, but I’m not sure if my specific use of the word makes sense to everyone.
Eons ago I wrote some stuff for another company (Beneath the Depths for Kenzer & Co’s Kingdoms of Kalamar - I think it’s now included in their major world book, or at least part of it is). We had similar thoughts on how gods should work, though they are stuck with that whole alignment issue. In their world, there are only a dozen or so gods, but they are interpreted differently in differently regions. I go a bit farther than they did in how different the gods might be region to region, though I have far more gods mucking up things on the mortal plane.
So what’s a pantheon? To me, a pantheon is a group of gods related by stories or myths. What does this mean? Well, if one god is seen as the son of two gods, then they must be in the same pantheon. If three gods are seen as brothers, then they and all their offspring are in the same pantheon. If a goddess is seen as married to a god, they are in the same pantheon. I include that last one, because I don’t want you to think it is only family or at least not simply blood relations. If there are no stories on how the gods are related, aligned or otherwise work together, then they are unlikely to be in the same pantheon. Gods known to be enemies are not necessarily in the same pantheons, but a less common example would be where the god of mercenaries was working against a pantheon right up until his employers sold him out. He joined the pantheon and is now their god of mercenaries.
So why does it matter? Well, it might not. On Fletnern, pantheons are most important when the pantheons go to war. So that means that gods can only be in one pantheon, right? Nope! If a god is in more than one pantheon they either need to stay neutral during the dispute or choose a side and assume that they are going to lose “membership” in the other pantheon. Does it matter if you lose your membership? Well, “exiled” gods (I cannot think of a better word, but I’m sure there is one) will likely find their religions outlawed and their shrines/temples torn down or rededicated to someone else.
So does every mortal fully accept that the gods are in multiple pantheons? No! Tell a worshiper in one region that they are worshiping the same god as someone in another culture is, and they are likely to get hostile. Tell a priest and you will at least be cursed. Just because the gods are above the petty squabbles of mortals doesn’t mean that these religious folks are. To the gods, the more worshipers the better, so there’s no reason to not reach out, especially when a neighboring pantheon seems to have a hole that their powers can fill.
Examples: Really quickly on this: Uilsilar is the god of agriculture (irrigation) in one region while being the god of a powerful river in another region. His power over the river is seen in how he keeps the chaotic river spirit (a water dragon) from flooding the farms, but allows it to flood in early spring to bring water and fertilizer to the fields. He’s an agriculture/irrigation god in both cases, but in one he’s a builder of canals and dams, and in the other a dragon defeating knight.
Meanwhile, Pento Tabochkis the judge of the dead. He is worshiped as Pento Tabochk by the humans, but as Zachoat by the orcs. In both cultures, he sits in the cavernous underworld and sends the dead down particular tunnels to arrive at their eternal rewards. This one is clearly seen as the same type of god, though they will fight bitterly as to whether he’s a human or an orc. (Gods are above such unimportant issues as race.)
What do I want you to take from this? Well, unspoken is that a pantheon needs to cover all the important aspects of life. If they don’t gods from other pantheons will start to “bleed in”. Gods can be in more than one pantheon. And lastly, you need to have a good heavenly brawl every once in a while. I have one brewing in Fletnern. If you follow my Fletnern stuff, you’ve seen some of the first signs of it, though no one can see it coming yet. The prophets will be notified soon.